keep your pool blue
DESCRIPTION
A how-to guide for homeowners with in-ground cement swimming pools. The chemistry of water balance for pools. If you take care of a swimming pool this manual is for you.TRANSCRIPT
KEEP YOUR POOL
BLUE____________
______________________________________________________________
THE CHEMISTRY OF BALANCING WATER
BY
STAN KINGSLEY
A Self-Published eBOOK
A Manual for Home Owners
written and published by
Stan Kingsley
A Digital Electronic Book
Available to All Without Charge as a PDF File
COPYRIGHTS AND PERMISSIONS
Copyright © 2012 by the author. All rights reserved.
For permission to reproduce or distribute for commercial gain or to publish in
some other format please contact the author by email at:
For questions and comments and if you would like to compensate the author
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Version 20120817 (August 17, 2012)
Non-fiction: How To, Swimming Pool Water Maintenance, Chlorination
Foreword
Because this book is a digital electronic file (pdf) viewable on your computer the
contents can be searched using the search function and sidebar. These functions vary
depending on which version of software you have. An outline of the contents follows.
Use key words or the title words to get to that section. A search labeled KEY POINTS
should list the pages summarizing each main topic.
The meat of the book is in the middle -- Achieving Balanced Water and
Maintaining Balanced Water. The earlier sections describe the basic chemistry and
definitions. Later sections have details about pool chemicals.
I first wrote this manual more than twenty-five years ago for myself. There was
not much written about pool care back then. Suppliers had started to provide written
information but, not unexpectedly, they had a slant which promoted their products, not
all of which were useful. Since that time computer aided analysis became widely
available in pool stores. I've updated the contents to reflect these changes as well as
new products. The most useful products and test procedures have remained the same
for a long time and are only aided by computers, not replaced by them.
There are many ways to purify pool water but I have selected only one,
chlorination, and have provided recommendations that balance economics with
convenience to make maintaining pool water less of a chore and less of an expense.
There are tens of thousands of technical pages written about water and its analysis
and water treatments. Even though the chemistry might seem complicated I have only
included enough to explain why certain effects happen in pool water. For further
information any topic today can be searched on the internet for more details.
In twenty-five years I have used only liquid and tablet chlorine along with acid
and baking soda (and occasionally calcium chloride because I live in a soft water
area). Nothing else is needed. Once a pool is balanced it is much easier and cheaper
to maintain it than it is to neglect it and fix it later. But even then a large dose of liquid
chlorine is usually all that is required plus balancing the calcium and pH. My pool has
always been blue.
It is also eco-friendly to maintain pool water in the most efficient ways possible.
The methods described in this manual should help you save time and money and help
the environment too. It is good to be "green" while keeping your pool water blue.
I am a retired scientist with degrees in chemistry and business administration. I
hope that what I have learned about pool water maintenance will be useful to you also.
The most practical points are collected in "key points" and I will start with a summary of
those.
/// *KEY POINTS* SUMMARY \\\
1.) If you are using chlorine to sanitize a swimming pool keep the pH near 7.4.
2.) There are two forms of economical chlorine -- solution (10%) and tablets (3" diameter).
3.) If stabilizer is present the chlorine will last longer but must be kept at a higher level. Too much stabilizer will throw off test results and interfere with chlorination.
4.) To preserve the cement the water must be balanced and the pH buffered. Hydrochloric acid and baking soda are the two chemicals needed for this.
5.) Calcium is required at about 300 ppm to preserve the cement and make water balance easier to maintain. Hard water requires adjusting other parameters.
6.) The best algaecide is liquid chlorine. Others are almost never required.
7.) Balanced water is blue, clear and odor-free.
8.) pH is the single most important test. It indicates the activity level of the chlorine.
9.) The only chemicals you need to use the methods described in this manual are chlorine tablets and solution, baking soda and acid. And calcium in soft water areas.
10.) Two necessary pieces of equipment are a pool thermometer and a comprehensive test kit which includes a nomogram for water balance.
Note: There is a short QUIZ at the very end. You may want to try it first.
Note: The "pool chemical data sheets" can be listed by typing the word data in thesearch window. They are good summaries of the chemicals and their use.
OUTLINE
INTRODUCTIONWhy Chlorine?It's All About Water BalanceIf In Doubt
CHLORINATION
CHLORINE SOLUTIONChemistry of Liquid ChlorineHandling of Liquid ChlorineKEY POINTS ABOUT CHLORINE SOLUTION
CHLORINE TABLETSChemistry of Trichlor TabletsHandling of Trichlor TabletsKEY POINTS ABOUT TRICHLOR TABLETS
CHLORINE POWDERChemistry of Calcium HypochloriteHandling of Calcium HypochloriteKEY POINTS ABOUT CALCIUM HYPOCHLORITE
STABILIZERProblems Caused By High Stabilizer ConcentrationKEY POINTS ABOUT STABILIZER
CONTROL OF pHDissociation of WaterDefinition of pHScale Of pH ValuesBufferingCorrecting Low pHWhy pH Increases And Alkalinity DecreasesCarbonate ChemistryKEY POINTS ABOUT pH CONTROL
CALCIUM BALANCECalcium Chloride: Chemistry and HandlingCalcium ConcentrationProblems with Hard WaterCalcium Balance and TemperatureCalcium Carbonate (Cement) SolubilityA Short Cut To Balance WaterUsing A NomogramSaturation IndexKEY POINTS ABOUT CALCIUM BALANCE
IDEAL CONDITIONS
WEATHER EFFECTSSeasonal Effects -- SummerSeasonal Effects -- WinterThe Effect Of RainEvaporationIncoming Water SupplyEnvironmentKEY POINTS ABOUT WEATHER EFFECTS
CONTROL OF ALGAESuper-chlorinationShock TreatmentOther Chlorine TreatmentsOther AlgaecidesQuaternary Ammonium ChloridesCost ComparisonKEY POINTS ABOUT CONTROL OF ALGAE
TESTING AND ADJUSTING POOL WATER
TEST KITSAccuracy of Test ResultsChlorine Test Methods: OTO vs. DPD
pH DETERMINATIONAcid DemandBase Demand
CHLORINE CONCENTRATIONChlorine MeasurementsEstimating Effective Chlorine (VERY IMPORTANT)Adjusting Chlorine
TOTAL ALKALINITY
CALCIUM HARDNESS
STABILIZER CONCENTRATION
TESTING CONDUCTIVITY
KEY POINTS ABOUT TESTING
SAMPLING THE WATER
RECORD KEEPING
CALCULATIONSParts Per MillionAmount of Chemical Additions
PARTIAL DRAINING OF THE POOL
OLD SCHOOL VS. NEW SCHOOL
POOL WATER PROBLEMSAlgaeAlgae With High ChlorineCloudy, Hazy WaterColored WaterFoamingOdorsHigh Dissolved SolidsHigh Filter PressureRough Deposits On Pool SurfacesCement Erosion
HOW TO AVOID BIG PROBLEMS
ACHIEVING BALANCED POOL WATER
MAINTAINING BALANCED POOL WATERSummer ProceduresOff-Season ProceduresOff-Season Time Saver
QUARTERLY TESTING TO MAINTAIN A BALANCED POOL
SEASONAL CHECK LIST
CHEMICAL SUPPLIES
KEY POINTS ABOUT MAINTAINING POOL WATER
EQUIPMENT CHECK LIST
FILTERINGCartridge FiltersDE FiltersPump Schedule
BRUSHING AND VACUUMING SKIMMER
PUMP TRAP
SAFETYRisks of Swimming In Chlorinated Water
COST ANALYSISPurchasing Chemical SuppliesCosts of TestingActual Annual Costs
POOL CHEMICAL DATA SHEETS
SUMMARY OF POOL CHEMICALS AND RECOMMENDED USES
QUIZ
/// INTRODUCTION \\\
This manual is for the home owner with a cement in-ground swimming pool. It
is a brief description of the necessary chemicals and procedures for using chlorine to
sanitize pool water. An attempt has been made to take the mystery out of the
chemistry.
Why Chlorine?
Chlorination has been used for over a century in public water supplies and
pools because it is safe and effective and low cost compared to the many other
methods which are not discussed here, such as bromination, ozonation, peroxides
and silver ions.
The three most widely used and readily available chlorine compounds are:
* Chlorine solution (sodium hypochlorite in water, very similar to bleach)
* Trichlor tablets (trichloro-s-triazinetrione powder in 3" tablet form)
* Calcium hypochlorite powder (granules similar to bleach)
What they are and how to use them is discussed in detail with suggestions for
making them the most effective at least cost to maintain your pool water. Comparisons
to other forms of chlorine are given.
It's All About Water Balance
Chlorination to kill bacteria and algae is the first step. The second aspect of
pool maintenance is water balance. It is necessary to control the pH by buffering the
water to keep it near neutral, slightly basic, so that it is never acidic and corrosive. The
third step is calcium balance to preserve the cement as long as possible.
If In Doubt
The suitability of the information in this manual and its application to particular
situations has to be determined by the reader. Always read the labels of the chemicals
before using and follow the instructions for safe handling and use. Consult a
professional when in doubt.
Now on to the technical stuff! There are explanations for the technical terms
and a simplified description of the chemistry. It may not seem simple to the average
pool owner without training in chemistry but the emphasis is on the basic mechanisms
at work in pool water treatment and why they affect decisions about which products to
use and how to use them. Each section is followed by KEY POINTS which are useful
for quick reference when it comes time to practice the art of water maintenance. They
are a summary of important points and recommendations. Without knowing the basics
it is easy to be led into wasting money on expensive materials when cheaper ones will
do or into chasing a problem around and around by attacking appearances rather than
true causes.
/// CHLORINATION \\\
The chemical species which sanitizes is hypochlorous acid, HOCl. It is the
active form of chlorine.
Chlorine compounds used in pools form hypochlorous acid when added to
water. The amount formed depends on the pH. In very acidic water all of the chlorine
will be in the active form. In basic water it remains inactive as hypochlorite ions. In
normal pool water the chlorine is a mixture of both active and inactive forms.
If this chemical terminology seems obscure it is only necessary to remember
that THE EFFECTIVENESS OF THE CHLORINE DEPENDS ON THE pH OF THE
WATER.
CHLORINE SPECIES IN WATER
Hypochlorous acid HOCl Active species, effective purifying agent
Hypochlorite ion OCl– Inactive species, becomes active at lower pH
Chloride ion Cl– Inactive species, forms salt
When testing for chlorine the test kit methods will indicate the sum of both the
active and inactive forms. The results can only be interpreted along with the pH value.
As described later the pH of pool water must be maintained in a narrow range for
several reasons. The amount of active chlorine will be anywhere from one-fourth to
three-fourths of the total when the pH is in the proper range. It increases when the pH
is lowered, that is, when acid is added.
TO OBTAIN A SUFFICIENT LEVEL OF ACTIVE CHLORINE IN POOL WATER IT
IS NECESSARY TO ADD A CHLORINE CONTAINING COMPOUND AND MAINTAIN
THE pH NEAR 7.4.
The three best materials for effective chlorination at low cost are described in
the next three sections. Each ends with a summary of KEY POINTS about that
material.
What Is The Right Amount of Chlorine?
It is often recommended that one part per million is sufficient. This is
approximately the amount of chlorine in most tap water. It might be OK for a short time
but it is so marginal that you would be constantly adjusting it upward. Pool books and
test kits often recommend three to five parts per million. This is a good range and
matches the range for most test methods for pool chlorine. When stabilizer is present
more chlorine is needed so I find that four to five or more parts per million is a more
practical chlorine level to aim for in swimming pools. This too can vary with the water
temperature, number of pool users and the weather. Public pools usually aim for ten
parts per million because they have so many users.
How Do You Know When You Have Enough Chlorine?
If algae shows up you need more chlorine. An immediate boost will kill the
algae and then a higher level in general will help prevent it from coming back. An
appropriate level of chlorine will prevent the appearance of algae on an on-going
basis. And, again, this depends on climate, weather and pool use. It is better to spend
a little more on regular chlorination and keep the level near four or five ppm rather
than have to shock the pool with ten or more parts per million.
/// CHLORINE SOLUTION (Sodium hypochlorite) \\\
Liquid chlorine is a ten percent solution of sodium hypochlorite (NaOCl) in
water. It is available in pre-packaged one gallon containers or in bulk at hardware or
pool supply stores. The bulk material is usually sold in two and a half gallon refillable
containers.
Chemistry of Liquid Chlorine
When liquid chlorine is added to a pool it immediately raises the level of
effective chlorine. Sodium hypochlorite is instantly converted to HOCl depending on
the pH, that is, the availability of acid ions (H+) in the water.
As acid ions are taken up to form the hypochlorous acid the pH of the pool
increases. This is one of the disadvantages of liquid chlorine because the pH must be
brought back to the desired range by the addition of acid to the pool water. Adding
hydrochloric acid lowers the pH and adds chloride ions (Cl–) which do not contribute
to effective chlorination.
Handling of Chlorine Solution
Liquid chlorine must be handled carefully. A splash can ruin your clothes. A
spill in your car would be a disaster. It is the same active ingredient as household
bleach but at double the concentration. Use caution when transporting or pouring
liquid chlorine.
HELPFUL HINTS: Use a box to keep the container from touching the car
interior. Carry the container without bumping it against yourself and only put it down
on something that will not be ruined by stray drips of the solution. Never mix the
solution with anything else. Only pour it into a clean measuring container. Avoid
breathing the vapors.
The ten percent concentration is only approximate. The storage life is limited so
the percentage will drop over time. Do not buy more than a season's supply at a time.
In spite of the inconveniences it is the most commonly used form of chlorine because it
is cheap and effective.
The change in chlorine level with the addition of chlorinating solution is
immediate. However, the level drops substantially within one or two days. This rate of
disappearance of chlorine is typical and depends on sunlight, temperature and the
presence of stabilizer and contaminants in the pool water.
Ten percent chlorine solution is added at about 500 ml (one pint) per day every
day to achieve a one part per million (ppm) chlorine level in a 15,000 gallon pool.
/// *KEY POINTS* ABOUT CHLORINE SOLUTION \\\
1.) The chlorine level is raised immediately as the solution is added.
2.) The chlorine protection only lasts a short time.
3.) The pool's pH rises when chlorine solution is added so it must be re-adjusted
with acid.
4.) Handle it carefully -- it is a hazardous material.
5.) It is the most cost effective form of chlorine.
6.) Use it for routine chlorination, superchlorination and shock treatments.
7.) The shelf life is limited.
/// CHLORINE TABLETS (Trichlor) \\\
The recommended stabilized chlorine is the three-inch tablet form of trichloro-s-
triazinetrione ("trichlor"). It is available under several brand names and all
manufacturer's labels include the following:
trichloro-s-triazinetrione 99.0%inert 1.0%available chlorine (89%)
Do not use stabilized chlorine with less available chlorine, such as "dichlor". Do
not confuse stabilized chlorine with tablets of calcium hypochlorite.
Comparing prices tablets are more expensive than liquid chlorine. This cost
difference is partially offset because trichlor tablets provide stabilizer. Also the trichlor
compound does not affect the pH and so reduces the requirements for acid.
Chemistry of Trichlor Tablets
Trichloro-s-triazinetrione is an organic compound which contains three chlorine
atoms per molecule. When these chlorine atoms are released they combine with
hydroxyl groups present in the water and form hypochlorous acid (HOCl). At the same
time three acid groups present in the water combine with the remainder of the trichlor
to form one cyanuric acid (CYA) molecule. Cyanuric acid is a stabilizer for chlorine. It
is discussed in the section on STABILIZER.
Chlorinating tablets are like time-release capsules. Chlorination is provided
over a long period of time at a slow rate. As the tablet dissolves the chlorine level
increases slowly and reaches a peak several days later. Most of the chlorine will be
released in the first two weeks. Three-inch tablets are preferred because it takes
about three weeks for them to completely dissolve.
Handling of Trichlor Tablets
They are easier to handle and transport than liquids. But if uncovered they give
off obnoxious fumes. It is best to wear rubber gloves when transferring tablets from
their original container to a pool dispenser. Or plastic tongs can be used to avoid skin
contact with the tablet.
Because they dissolve slowly the three inch tablets eliminate the need for daily
attention. The best way to control the rate of chlorination is to use a floating dispenser
which can be loaded once a week.
Three-inch tablets are added two tablets per week to achieve about one ppm
chlorine in a 15,000 gallon pool.
/// *KEY POINTS* ABOUT TRICHLOR TABLETS \\\
1.) When trichlor tablets dissolve they slowly create hypochlorous acid (the effective form of chlorine).
2.) Stabilizer (cyanuric acid) is also released but at one-third the rate of the hypochlorous acid.
3.) Continuous use of trichlor tablets causes the amount of cyanuric acid stabilizer to increase.
4.) Limit use to avoid excess stabilizer.
5.) Use tablets during the hottest time of the year for routine chlorination.
/// CHLORINE POWDER (Calcium hypochlorite) \\\
A third type of chlorine which is useful in pools is calcium hypochlorite. Its
physical form is solid, usually a powder. It can also be found as tablets, but do not
confuse it with trichlor tablets. Look for the following description on the label:
calcium hypochlorite 65%inert ingredients 35%available chlorine (65%)
The cost of calcium hypochlorite varies with quantity and packaging, from 100
pound drums to 25 pound pails or one pound packages.
Chemistry of Calcium Hypochlorite
When calcium hypochlorite is added to a pool it raises the level of effective
chlorine as it dissolves and it raises the pH. Its chemistry is similar to liquid chlorine
but with calcium in place of sodium. The addition of calcium to the pool water is an
advantage in most cases unless the water is hard meaning that there is already a high
level of calcium in it. See the section CALCIUM BALANCE for problems with hard
water.
Handling of Calcium Hypochlorite
Calcium hypochlorite is easier to transport than liquid chlorine and easier to
handle than trichlor. The shelf life is substantially longer than that of chlorine solution.
A disadvantage of calcium hypochlorite is that it causes cloudy pool water until the
filter removes residual particles.
The level of chlorine is raised quickly as the powder dissolves. The denser
forms (tablets or cartridges) will be slower to dissolve and are added less often. They
behave like time release capsules.
The powdered form of calcium hypochlorite can offer an advantage when used
as a shock treatment to kill algae. The powder can be sprinkled on or near algae
spots. When this is done in still water the concentration of chlorine becomes very high
right where the algae is. Some powders are finer and dissolve faster providing a
quicker shock and some are 75% active.
One pound of 65% active powder provides a 5 ppm chlorine shock in a 15,000
gallon pool.
About three ounces per day of calcium hypochlorite powder in a 15,000 gallon
pool will provide about one ppm chlorine.
/// *KEY POINTS* ABOUT CALCIUM HYPOCHLORITE \\\
1.) The powder form of calcium hypochlorite quickly raises the effective chlorine concentration.
2.) The tablet or cartridge form of calcium hypochlorite slowly releases effective chlorine.
3.) It causes the pH to go up.
4.) It provides calcium, necessary for pool water, but a problem in hard water areas or when calcium content is already high.
5.) The powder form is an excellent algaecide, especially for spots or clusters of algae.
COMPARISON OF CHLORINE COMPOUNDS
Name: Sodium Calcium Trichloro-s-hypochlorite hypochlorite triazinetrione
Formula: NaOCl Ca(OCl)2 (CNOCl)3
Form: Solution Powder Tablet (3")
% Active: 10% active 65 to 75% active 99% active
Provides: HOCl HOCl, calcium HOCl, stabilizer
Chlorination: Excellent Good Excellent
Use rate: 16 oz daily 3 oz daily 16 oz weekly
Shock: Excellent Good Not recommended
Spot algaecide: Not recommended Excellent Not recommended
/// STABILIZER (Cyanuric acid) \\\
Chlorine compounds decompose when exposed to sunlight (ultra-violet
radiation). This happens to hypochlorous acid in pool water. Cyanuric acid (CYA)
stabilizes hypochlorous acid and extends its lifetime. Stabilizer concentration should
be kept under 100 ppm. About 30 ppm is optimum. A good starting range is 20 to 40
ppm. Higher amounts are required in summer along with higher chlorine
concentrations. Indoor pools do not require stabilizer.
When trichlor tablets are used stabilizer is formed as they dissolve. If trichlor is
not used cyanuric acid stabilizer can be added separately. For example, adding five
pounds would provide 40 ppm in a 15,000 gallon pool. (See the sections on
CALCULATIONS and ADDITIONS TO THE POOL.) Cyanuric acid is sometimes called
conditioner but it acts as a stabilizer.
When trichlor tablets are added routinely to the pool the amount of cyanuric acid
(CYA) will increase by about 3 ppm per month. This effect is very important. Because
the cyanuric acid (CYA) level can become excessive if using trichlor continuously at
least twice a year determine its concentration. If it is too high then one of the other
non-stabilized forms of chlorine should be used instead of trichlor until the level of
CYA comes down below 50 ppm. Be aware that other forms of chlorine may be
stabilized and their use will increase the CYA levels in your pool.
Problems Caused By High Stabilizer Concentration
If the CYA level becomes too high it will interfere with the activity of the chlorine.
The test kit results can show adequate levels of chlorine but there may still be algae
growth. If the pool is super-chlorinated the level of chlorine will remain very for a very
long time during which it should not be used.
Cyanuric acid (CYA) is very useful but only at a reasonable level. Any amount
over 100 ppm is too much. It is better to never exceed 60 ppm. If the level of CYA is
very high there is only one way to reduce it: Drain about half the pool and refill to cut
the concentration in half. Caution: See the section: Partial draining of the Pool. In
less severe cases simply stop using the trichlor type of chlorine -- the stabilizer
concentration will drop by about 7 ppm per month.
High cyanuric acid (CYA) levels also interfere with the test for alkalinity. At less
than 30 ppm the effect on the alkalinity test is small enough to be ignored. But in large
amounts CYA can mask a low level of bicarbonate alkalinity. See the section TOTAL
ALKALINITY in TESTING AND ADJUSTING POOL WATER.
For these reasons it is recommended that trichlor be used for only four months
of the year to avoid excessive build-up of stabilizer, cyanuric acid.
/// *KEY POINTS* ABOUT STABILIZER \\\
1.) At about 30 ppm it extends the lifetime of chlorine.
2.) Too much stabilizer inhibits the effectiveness of chlorine.
3.) Stabilizer contributes to alkalinity in the test for total alkalinity.
4.) Too much of it will mask a deficiency in carbonate level unless the alkalinity test result is corrected for it.
5.) The amount of cyanuric acid in the pool water increases when stabilized chlorine is used continuously for long periods of time.
6.) When the stabilizer level is high do not use trichlor (or any stabilized chlorine product); use sodium or calcium hypochlorite instead.
/// CONTROL OF pH \\\
Dissociation of Water
Water is unstable and to a very small degree its molecules dissociate. They
break down into ion pairs -- one hydrogen ion (H+) and one hydroxyl ion (OH-). The
balance between (H+) ions and (OH-) ions is easily influenced by other molecules. If
the balance favors the (H+) ions the water is acidic. When the amounts of (H+) ions
and (OH-) ions are equal then the water is neutral. If the (OH-) ions predominate then
the water is basic. A chemist would describe the dissociation as follows:
H2O = (H+) + (OH–)
water forms hydrogen ions and hydroxyl ions
(acidic) (basic)
Definition of pH
The balance between the dissociated ions is referred to as "pH." It is measured
on a scale which runs from zero to fourteen. (It happens to be the negative logarithm
of the concentration of hydrogen ions (H+) expressed in moles per liter.) Because of
the way it is defined neutral water has a pH of 7. Acidic water is less than seven, down
to zero. Basic water has a pH over 7 up to 14. The pH value is the strength of the
hydrogen ion concentration. It is an abbreviation of the German phrase "potenz
Hydrogen," literally "power of hydrogen."
Scale Of pH Values
neutral
0----------------------------------7---------------------------------14
acidic basic
For swimming pool water the desired range of pH is within 7 to 8, always on the
slightly basic side. Acidic pool water would be corrosive. Above pH 8 there would be
very little of the active form of chlorine. Recall that hypochlorous acid becomes
inactive hypochlorite ion in strongly basic water.
For these reasons the ideal value of pH is around 7.4 (with an acceptable range
of 7.2 to 7.6) where the water is not corrosive and about one half of the chlorine will be
in the active form.
Buffering
Buffering is a method of slowing down changes in pH. Materials are added to
the water which will counteract increases or decreases in the pH. In swimming pools
this is accomplished by adding baking soda (sodium bicarbonate).
The amount of baking soda required is about one hundred ppm, primarily to
prevent cement corrosion (see CALCIUM BALANCE) but also to provide buffering
action for pH stability. The level of sodium bicarbonate will change relatively slowly
and can be adjusted about every two weeks. It is checked with a test for total alkalinity.
The pH has to be adjusted more often. In buffered swimming pools the normal
drift will be to higher pH. Also, as described earlier the use of sodium or calcium
hypochlorite will raise the pH. These changes are corrected by the addition of acid.
Most commonly muriatic (hydrochloric) acid is used. It is more cost effective than dry
acid (sodium bisulfate). The pH adjustment with acid should always be the last thing
done when treating pool water. (See below.)
Correcting Low pH
Acid additions should always be done such that the pH never goes below 7.
However, if the pH should accidentally go below 7 it can be corrected in several ways:
*A slightly acidic pool just under pH 7 can be corrected by adding liquid or powder chlorine (sodium or calcium hypochlorite).
*A pool with mildly acidic water (pH about 6) can be corrected by adding baking soda.
*Sodium carbonate (Na2CO3) can be used to adjust a very low pH pool. This material is sold under various names for raising pool pH. It should never be needed but if the occasion arises a pool store would be able to provide it. There is no need to keep it on hand.
Why pH Increases And Alkalinity Decreases
Acids and bases (alkaline materials) neutralize each other and form salts. In
pool water the acid and bicarbonate combine to form carbonic acid. Carbonic acid
decomposes to water and carbon dioxide gas. When this happens the carbonate and
acid ions are lost. All that remains is sodium and chloride, salt. The decrease in
carbonate reduces the alkalinity. The decrease in acid raises the pH. The
accumulation of salt raises the total dissolved solids.
All of these changes are unavoidable and this is why the baking soda and acid
must be replenished. All of this happens faster when the temperature is higher. To
minimize the neutralization of baking soda by the acid it is best to adjust alkalinity first
and then adjust the pH. Doing this in the other order can result in a never-ending
consumption of both materials as they are converted into salt.
Carbonate Chemistry
The chemical formula for sodium bicarbonate is NaHCO3.
In water it provides bicarbonate ions (CO3–), carbonate ions (CO3– –) or
carbonic acid (H2CO3) depending on the pH.
Each carbonate ion can take up two acid ions and bicarbonate can take one.
This is why sodium carbonate will more effectively raise pH.
The pH of carbonate is 11 and the pH of bicarbonate is 8.5 in unbuffered water.
At pH three both of them are completely converted to carbonic acid.
At normal pool pH values the buffering system is actually a bicarbonate/
carbonic acid mixture. This happens because the pool pH lies between the pH's of
these two species. It doesn't matter whether bicarbonate (baking soda) or carbonate
(soda ash) is added to the pool water. Once the pH is adjusted to the normal range of
7.2 to 7.6 the same species are formed. This is the reason that there is no need for
carbonate addition and the less expensive baking soda is used.
/// *KEY POINTS* ABOUT pH CONTROL \\\
1.) Because it determines the effectiveness of chlorine pH is the most important item to control to maintain pool water.
2.) A pH of 7.4 is the best value (as a high in summer and as a low in winter).
3.) The usual range is 7.2 to 7.6 for pH.
4.) Almost always the pH will drift higher.
5.) Hydrochloric (muriatic) acid is used to adjust the pH back to lower values.
6.) Adjusting pH should always be done after making all other additions to the pool water.
7.) Maintenance of pH is often a daily task (in season).
8.) Baking soda is used to retard changes in pH.
9.) Determining the baking soda content (the total alkalinity test) should be done about every two weeks.
10.) The correct amount of baking soda (bicarbonate alkalinity) is about 90 ppm. (It will vary with temperature and calcium content. See the section on CALCIUM BALANCE.)
/// CALCIUM BALANCE \\\
In-ground swimming pools are usually made by casting concrete over a metal
frame of reinforcing rods. The interior surface of the pool is finished with a coating of
cement containing marble dust ("plaster") to give it a bright white color. Concrete,
cement and marble are principally or entirely limestone which is the mineral name for
calcium carbonate.
The pool surface in contact with water is going to slightly dissolve and put
calcium and carbonate in the water. To prevent the cement surfaces from eroding
calcium and carbonate should be added to the pool water.
Carbonate is supplied when baking soda (sodium bicarbonate) is added. See
the section on CONTROL OF pH. Calcium is provided by the addition of calcium
chloride.
Calcium Chloride: Chemistry and Handling
Calcium chloride is a chemical similar to ordinary salt. It absorbs moisture so it
is usually available in its hydrate form, calcium chloride dihydrate (at 80%, mixed with
other chlorides). Higher purity pellets are also available.
The chemical formula is CaCl2.2(H2O).
It can be purchased as a brand name product or in bulk form. Hardware supply
stores offer large bags of bulk calcium chloride at lower prices per pound. Smaller
quantities or brand name products will cost more.
The best way to add calcium is to fill a clean five gallon pail with pool water and
add a few pounds of calcium chloride. When it dissolves it gives off heat. The solid
material or its hot concentrated solution can be irritating to skin. Carefully pour the
calcium solution into the skimmer leaving any solid materials in the bottom of the pail.
Repeat this procedure until the required amount of calcium has been dissolved and
added. Or flakes of calcium chloride can be added slowly to the skimmer so that they
dissolve before reaching the pump.
Calcium Concentration
A calcium concentration near 300 ppm is best. A suitable range is 200 to 400
ppm. When the calcium level is controlled fairly closely it is easier to maintain the
proper chemical balances. Testing every three months will usually be sufficient. A
new pool or one recently resurfaced may change more quickly than an older pool and
not need additional calcium for a long time.
It is important to remember that the routine use of calcium hypochlorite will add
significantly to the calcium level of the pool water. See the section on CHLORINE
POWDER. Its use as an algaecide or for shock treatments will not contribute much to
the calcium level -- about 2 ppm per treatment. However, routine chlorination with this
material will add about 20 ppm per month. This is not a problem for most pools and
simply reduces the requirement for adding calcium chloride. For pools with an existing
high level of calcium, calcium hypochlorite must be avoided.
Problems with Hard Water
High calcium levels can be the result of naturally occurring levels in the
incoming water used to fill the pool. Some water supplies are naturally "hard" and can
contain so much calcium that scaling becomes a problem. This happens when
calcium carbonate precipitates out of the pool water as a hard rough deposit on the
walls of the pool. Often high calcium content can be compensated by altering
carbonate concentration and pH. In areas where the problem is severe it may be
necessary to bring in water with a lower calcium content from another location.
The presence of calcium (and similar ions such as magnesium) is said to make
water "hard" because it interferes with the sudsing action of detergents. In some test
kits the calcium determination is referred to as a "water hardness" or "calcium
hardness" test.
Calcium Balance and Temperature
Temperature changes the solubility of chemicals in water. In particular the
solubility of calcium carbonate will change. As its temperature changes it is possible
for pool water to become corrosive and dissolve the cement. Or it is possible that
calcium carbonate will begin to precipitate. This can cause cloudiness in the water,
scale formation on equipment or rough deposits on the walls of the pool.
This problem was addressed by chemists who developed a saturation index for
calcium carbonate. It is a way of calculating the amount of calcium and carbonate
needed for a given pH and temperature to prevent corrosion (dissolving cement) and
scaling (precipitating calcium carbonate).
Calcium Carbonate (Cement) Solubility
Most minerals are more soluble in warm water than cold. Calcium carbonate is
unusual in this respect -- it becomes less soluble as the temperature increases. This is
why a lower carbonate (lower alkalinity) level is necessary in hotter weather. And the
acidity should be higher (lower pH) in warmer water because of the decreased
solubility of the calcium carbonate.
One approach for counterbalancing the solubility of the cement requires
changing the pH to compensate for temperature changes. The calcium and carbonate
concentrations are kept constant. A set of conditions satisfying these requirements is
given below:
BALANCED WATER CONDITIONS
Water temperature (ºF) 85º 60º
Calcium (ppm) 300 300
Alkalinity, total (ppm) 90 90
pH 7.3 7.5
Note that the alkalinity is the same and the calcium concentration is the same.
The change in water temperature is compensated by altering the pH. Over a wide and
useful range of temperature the water can be balanced with the calcium concentration
near 300 ppm. The total alkalinity shown above includes 80 ppm for carbonate
alkalinity and 10 ppm for the effect of stabilizer.
This shows that it is particularly helpful to keep the calcium level near 300 ppm.
With this level of calcium the pH can be kept in the range where the chlorine is
effective.
Another way to look at the problem of balancing the water is given below.
A Short Cut To Balance Water
Calcium balance is complicated because there are four items to be concerned
about. With two of these kept in a narrow range -- calcium around 300 ppm and the
pH around 7.4 -- the problem is simplified. Now it is only necessary to alter the
carbonate alkalinity to suit the temperature.
In the range of 60 to 90ºF the alkalinity can be adjusted as shown below:
BALANCED WATER CONDITIONS AT pH 7.4
Temperature (ºF) Total Alkalinity (ppm)
90 75
80 85
70 100
60 115
For most pools this is a good approach because alkalinity can be easily
changed in response to seasonal temperatures. Since calcium levels are slow to
change it is easier to maintain them at a uniform level. The pH is restricted to a narrow
range because of its effect on chlorine.
For a heated pool kept at constant temperature the problem of calcium balance
is much simpler. A carbonate level can be selected for the given temperature and a
pH of 7.4. It is still necessary to test and adjust the pH, calcium and carbonate to
maintain the selected levels.
For pool water which is hard it is necessary to use a calcium to carbonate ratio
outside the normal range. And sometimes the temperature falls outside the range
covered in the table above. In these cases a nomogram will make it easier to find the
right amount of alkalinity to use.
Using A Nomogram
The word nomogram is a combination of Greek words meaning a law which is
written or drawn, in this case a scientific law which describes the solubility of calcium
and carbonate as determined by the temperature and pH.
A good test kit will include a nomogram which is a way to compare these four
items. The nomogram could be a series of tables or more conveniently it will be a
device like a slide rule. A test kit which includes a nomogram for water balance is well
worth the cost.
The nomogram will cover a wide range of conditions but only those which keep
the pH between 7 and 7.6 are of interest. It is best to start with the water temperature
and set it against a pH of 7.4 Next find the alkalinity which compensates the existing
calcium level. If the calcium level is less than 220 ppm consider adjusting it to 300
ppm and find the amount of alkalinity to balance it. Once the alkalinity has been
selected it can be maintained until there is a large temperature change.
The nomogram is especially useful if your water supply is hard and has a
calcium level higher than 400 ppm. In this situation locate the value of the calcium
level and find an alkalinity value which will balance the water at a useful pH for the
given temperature. Since it is not easy to lower calcium it will be necessary to adjust
alkalinity to lower levels to compensate for it. In this way the necessary pH can be
maintained for effective chlorination over the seasonal temperature range of the pool.
Saturation Index
The saturation index, also called the Langlier index, is a measure of the water
balance. It is the difference in the pH of your pool water compared to the pH at which
calcium is saturated at the temperature and alkalinity of your pool water. Most
computer analyses of pool water will include a value for the saturation index. It is the
single most comprehensive indicator of how well your water is balanced. When the
difference between your pool's pH and the pH of saturation for calcium is zero your
pool water is perfectly balanced.
An acceptable range for the saturation index is plus or minus 0.3 pH units.
When your pool's pH is greater by 0.3 pH units that condition can lead to scaling, the
precipitation of calcium as hard lumps on the pool surfaces. When your pool's pH is
less by 0.3 pH units that condition is corrosive. So at a saturation index over +0.3 you
need to add acid to lower the pH. When the saturation index is under --0.3 you need
to add baking soda. The computer's computation of the saturation index is only as
good as an accurate measure of pH, temperature, alkalinity and hardness.
/// *KEY POINTS* ABOUT CALCIUM BALANCE \\\
1.) Calcium is necessary to preserve the cement finish of the pool surfaces.
2.) The desired range for calcium is 200 to 400 ppm.
3.) Calcium hardness should be determined at least four times a year. A new or
recently resurfaced pool should be checked more often.
4.) The amount of calcium and the amount of carbonate necessary to preserve the
cement depend on the pH and the water temperature.
5.) If the pH is kept near 7.4 and the calcium concentration is near 300 ppm then
the alkalinity can be adjusted to compensate for seasonal changes in the water
temperature.
6.) The desired amount of alkalinity can be determined from a set of tables (or a
nomogram) which compares levels of calcium and carbonate with pH and
temperature.
7.) My personal preference is to keep the calcium concentration on the high side
at about 500 ppm so that the alkalinity and pH can be kept lower during the
summer.
/// IDEAL CONDITIONS \\\
There are two materials which are necessary for water maintenance using the
method described in this manual: CHLORINE -- to disinfect the water, and CALCIUM
-- to preserve the cement.
Chlorine effectiveness depends on pH and stabilizer. Calcium solubility
depends on pH and carbonate alkalinity.
The ideal values for these items and the acceptable ranges are given below:
Ideal Range
Chlorine (effective) 2 ppm 1 - 3 ppm
Stabilizer 25 ppm 10 - 40 ppm
pH (to activate the Cl) 7.4 7.2 - 7.6
Calcium 300 ppm 200 - 400 ppm
Carbonate alkalinity 80 ppm 60 - 120 ppm
Total alkalinity (test kit) 90 ppm 70 - 130 ppm
Total alkalinity is shown separately from carbonate alkalinity because it is the
one actually measured and it differs because of the influence of the stabilizer.
The "ideal" water temperature for ideal conditions is 77ºF. Since water
temperature can vary or be set to a different value there has to be a range of
acceptable values for the other parameters.
In warmer water the chlorine and stabilizer requirements are higher. The pH
should be slightly lower (more acidic). The carbonate alkalinity should be lower. The
calcium can be maintained near 300 ppm.
In cooler water the chlorine and stabilizer requirements are lower and
maintaining lower levels will reduce costs. The pH can be kept slightly higher (less
acidic) which also reduces the cost. The carbonate alkalinity should be higher. The
calcium can be maintained near 300 ppm.
Although calcium balance allows for some variations in the concentrations of
calcium and carbonate a minimum carbonate alkalinity of 60 ppm and maximum
calcium level of 600 should be observed.
Remember that ideally the saturation index (Langlier index) will be zero with an
acceptable range of plus or minus 0.3 pH units. That measure is a combination of the
temperature, pH, calcium hardness and carbonate alkalinity. A computer can provide
the calculation for it.
/// WEATHER EFFECTS \\\
Even in a stable climate (such as Florida) pool water can change from below
60ºF in winter to above 90ºF in summer. It is important to have a pool thermometer. As
shown above in IDEAL CONDITIONS calcium balance, buffering and chlorination all
depend on water temperature.
Seasonal Effects -- Summer
When the water is 20ºF warmer changes occur twice as fast -- algae and
bacteria breed faster, stabilizer decomposes faster, bicarbonate and acid neutralize
faster -- and there is more use of the pool in hotter weather. The most direct ultra-violet
radiation occurs at the summer solstice (June 22 in the northern hemisphere). These
conditions cause changes in the requirements to maintain balanced water.
The chlorine and stabilizer levels have to be kept higher to avoid depletion
because the consumption of chlorine is greater. The pH can be adjusted to lower
values (7.2 to 7.4) to make the chlorine more effective. The alkalinity can be kept at
the lower end of its range (60 to 80 ppm). This will be more compatible with a lower
pH and reduce acid demand. These changes will make the precipitation of calcium
carbonate less likely during very hot weather.
Seasonal Effects -- Winter
When water temperatures drop (especially below 60ºF) there is much less
demand on the chlorine. If the pool is kept open chlorine can be kept lower at one
ppm and the pH kept at 7.4 to 7.5. Higher alkalinity is required (120 ppm). Stabilizer
concentration should be lower, near the winter solstice, December 22. Cold weather
is an opportunity to reduce costs because less chemical treatment is needed.
The Effect Of Rain
Rain upsets balanced water. It carries dust, dirt, organic matter, pollen, algae
and bacteria into the pool. This causes more of the chlorine to be used and the pH to
rise. The cure for this is simple -- add liquid or power chlorine, then adjust the pH.
The pH of rain is near 5 or 6. It is acidic because it combines with carbon
dioxide in the air and forms carbonic acid. Buffered pool water overcomes this pH
difference; in fact the pool pH becomes less acidic because of the materials carried
along with the rain.
For a typical pool a half inch of rain will be about one percent of the volume;
dilution is not great unless there is a downpour. Heavy rain will require draining some
water and adjusting chlorine, alkalinity and pH (in this order). If possible it is best to
have the pool water circulating during rain.
Evaporation
In windy, dry, hot conditions an outdoor pool exposed to the sun could lose
several inches of water in a week. Normal evaporation is less than this and with luck
rain will balance losses. When luck does not prevail it will be necessary to add water
to the pool.
Incoming Water Supply
Residential water supplies can vary depending on the geographic location.
Test the water supply with a pool test kit. This is especially useful when filling a pool.
It is important to remember that municipal water supplies are treated and have
alkalinity and calcium levels that can be substantial. Most municipal water
departments will share their test results.
A typical comparison of tap water, pool water and rain is shown in the table
below:
WATER SUPPLY COMPARISONS
Tap Water Pool Water Rain
Chlorine, free (ppm) 1 2 0
pH 9.5 7.4 5
Alkalinity, total (ppm) 60 95 0
Calcium (ppm) 80 300 0
Stabilizer (ppm) 0 25 0
Environment
Proximity of trees, plants and uncovered soil will affect the amount of dust,
leaves, pine needles, pollen and organic matter blown into the pool. A screen pool
enclosure will greatly reduce the amount of contamination. Careful selection and
placement of decorative plants and the use of mulch or stone near the pool perimeter
can also reduce cleaning chores.
/// *KEY POINTS* ABOUT WEATHER EFFECTS \\\
1.) Rain upsets balanced water requiring additional chlorine and acid.
2.) Hot summer weather increases the need for chlorine; alkalinity and pH should be kept at the lower end of their acceptable ranges.
3.) Cold winter weather is an opportunity to save chemical supplies since demands on chlorine are lower and the pH can be higher.
4.) With more intense sunlight (near the summer solstice) more chlorine and stabilizer are required.
/// CONTROL OF ALGAE \\\
The most common pool problem is algae growth. Even a brief lapse in
maintaining the chlorine level or the pH can result in algae blooms, especially after a
rainy or windy day.
One of the most effective algaecides is chlorine. It is also the cheapest and
should be the first choice among the methods to combat algae growth.
Super-chlorination
Bringing the chlorine concentration to a higher than normal level is called
"superchlorination." Because it immediately raises chlorine levels the use of liquid
chlorine provides the best effect. When the first bloom of algae growth is noticed
doubling the normal chlorine level will often kill it. This treatment should be
accompanied by brushing the pool surfaces. The filter will remove the dead algae.
The pool should not be used until the chlorine level returns to the normal range.
Occasional superchlorination will also remove combined chlorine which builds
up when waste material is disinfected. It is convenient to do this when the pool will not
be in use for a day or two. Ideal times to super-chlorinate are when rain is expected or
if going on a short trip and leaving the pool unused.
Shock Treatment
If there is a lot of algae or if it resists superchlorination then a larger dose of
chlorine can be used. This is called "shocking " the pool. Again liquid chlorine is an
excellent way to increase chlorine levels immediately to a high value. The amount of
chlorine to use depends on the severity of the problem. Most often 30 to 60 ppm will
take care of a major algae bloom. This is ten to twenty times the usual amount so it
will take a while for the chlorine to return to normal. Do not use the pool until the
excess chlorine has dissipated.
To make superchlorination or shock more effective the chlorine compound can
be added at the end of the day when the water is not circulating. First adjust the pH to
7.2 before turning off the pump. Then add the chlorine to the water along the
perimeter of the pool. During the night the chlorine level will be highest near the walls
where most algae usually forms. The next morning the pH can be checked after
circulating the pool water for half an hour and adjusted as necessary. Note that
superchlorination will usually boost chlorine for about two days whereas shock
treatment will take several days longer.
In pools which are seldom used or used by one person the need for shock
treatment is rare. In pools which are used by many people, especially in hot weather,
superchlorination and shock will be needed more frequently. Shocking the pool water
is usually required only if the maintenance has been neglected. In a well maintained
pool it would never be required. But if the pool water turns dark green it is definitely
time to shock treat the water. If a pool is going to be left unattended for a period of time
preventive shock treatment can be used to avoid algae growth.
Many times when a pool has a strong odor it is not the chlorine that causes it but
rather the by-product of chlorine and urine which is chloramines. This should
definitely be treated by superchlorination or shock.
Other Chlorine Treatments
In addition to sodium hypochlorite solution there are three powders which are
also very effective algaecides:
(1) Calcium hypochlorite. See the section CHLORINE POWDER. This
material is an excellent choice for control of algae spots. It can be applied directly in
the vicinity of the algae when the pool is not circulating to raise the chlorine level very
high in a localized area.
It is also very good for superchlorination and shock. Since it is chemically
similar to liquid chlorine it will require pH adjustment in the same manner.
(2) Trichloro-s-triazinetrione (trichlor) powder. This is the same material as
discussed in the section CHLORINE TABLETS. Powered trichlor is sold specifically as
a treatment for "black algae." It could harm the cement surface.
(3) Lithium hypochlorite. It is an excellent material but very expensive. It
could be used if both calcium and stabilizer levels were too high preventing the use of
either of the other two powders.
NOTE: Using spot algaecides should be avoided since strong solid chlorine
compounds can dissolve cement surfaces weakening them and making them rougher
which then promotes algae growth. The first attempt to kill algae should use liquid
chlorine then powders can be used with the water circulating. Spots of algae can also
be brushed with a stainless steel brush to help break them open.
Other Algaecides
Before buying a high priced algaecide it is a good idea to check the label. If it is
just an expensive form of chlorine it will not be any more effective than the cheaper
forms. There are some very exotic algaecides available and they have higher costs.
Before resorting to these materials it is better to try shocking the pool with liquid
chlorine. Then try powdered chlorine compounds applied in the area of the algae
colony. If these attempts do not kill the algae consult a pool store about the problem
for a recommendation about one of the more specialized types.
Quaternary Ammonium Chlorides
There is a family of common algaecides known as quaternary ammonium
chlorides (also called "alkyl ammonium chlorides"). They are available from several
manufacturers as ten percent solutions in one gallon containers. At higher cost this
material provides an alternate way to defend against algae and bacteria which is
chemically different from chlorination. A small addition each week of a quaternary
ammonium chloride solution is an optional preventive measure. The use of this
material imparts a slippery feel to the water which may be unwanted. With larger
amounts foaming will occur. They are not recommended.
Cost Comparison
The relative costs of these algaecide and shock treatments are listed below.
The prices are in dollars per pound of active ingredient (which is not the same as the
shelf price in the store). The prices of almost all of these items have gone up since this
list was prepared but the comparisons are still valid. Currently liquid chlorine prices in
Florida have doubled as I type this but the list still shows the expected relative
expense of each type of chlorine.
Sodium hypochlorite solution, bulk (2.5 gallon jug) 1.00
" " one gallon, prepackaged 1.70
Calcium hypochlorite (powder) 3.00
Quaternary ammonium chlorides (solution) 5.00
Trichloro-s-triazinetrione (trichlor), powder 7.50
Lithium hypochlorite (powder) 20.00
It is easy to see that sodium hypochlorite should be the first choice for shocking
or super-chlorinating. The calcium hypochlorite at slightly higher cost is a useful
alternative.
Fighting algae is always a situation where an ounce of prevention is worth a
pound of cure. And a dollar's worth of chlorine is better than a more expensive
algaecide.
/// *KEY POINTS* ABOUT CONTROL OF ALGAE \\\
1.) The most cost effective algaecide is chlorine solution, ten percent sodium
hypochlorite: One gallon provides 5 ppm chlorine in 15,000 gallon pools.
2.) For algae on the bottom of a pool a chlorine powder is more effective, added
when the water is still. The most cost effective powder is calcium hypochlorite:
One pound provides 5 ppm chlorine in 15,000 gallon pools.
3.) Expensive algaecides are not more effective and usually not required.
Note: My personal preference for treating algae or stains on the bottom of a pool is
to use chlorine solution instead of a powder. The liquid chlorine can be
applied by pouring it through a tube such as the brush pole, with the brush
and handle removed. This requires some dexterity, and a funnel helps, but
it puts liquid chlorine at high concentration right at the place where it is needed.
Obviously, the pool water should not be circulating while doing this.
Note: Algae is air-borne. It is always present. You can control it so that it is not
visible, but it is never completely absent from a pool.
/// TESTING AND ADJUSTING POOL WATER \\\
TEST KITS
A test kit is the most important piece of equipment needed for maintaining pool
water. There are many available. It is very advantageous to purchase a kit that
includes all five of the necessary tests:
pH determinationchlorine concentrationtotal alkalinitycalcium hardnessstabilizer concentration (cyanuric acid)
Accuracy of Test Results
If in doubt about the accuracy of a test repeat it with new reagents. The cost of a
second test is small compared to the trouble that comes with inaccurate test results. If
the actual pH is higher than indicated the chlorine is less effective. Or, if the pH is
actually lower the water could be corrosive to the cement. The test kit and its reagents
should be stored indoors out of direct sunlight. It does not have to be refrigerated.
Chlorine Test Methods: OTO vs. DPD
There are two methods for measuring chlorine commonly available in pool test
kits. They are referred to as "OTO" and "DPD" which are abbreviations for the reagents
used in the test. The DPD method offers the advantage of using two separate steps to
find the free and total chlorine levels. The OTO test indicates free chlorine for a few
seconds after which total chlorine is indicated. They both provide satisfactory results
but the DPD method is easier to interpret.
pH DETERMINATION
The pH determination indicates the basicity of the pool water. Refer to the
section on CONTROL OF pH. Test kits are designed so that the appropriate pH level
will be approximately in the middle of the test kit range. In a normal buffered pool the
pH will drift to higher values and it will be necessary to bring it back down by adding
acid.
Acid Demand
The amount of acid required is often referred to as "acid demand." For example,
the amount of acid required to change the pH from 7.8 to 7.3 in a 15,000 gallon pool
with 100 ppm of carbonate alkalinity is 325 ml (ten ounces) of concentrated
hydrochloric acid (muriatic acid). This amount can be calculated based on the
chemical interactions of the bicarbonate buffer and the acid.
Fortunately it is not necessary to calculate acid demand each time the pH
changes. Large test kits include a test for this and a table for determining how much
acid should be added. Drops of a standard acid solution ("acid demand reagent") are
added to the pH sample until the desired pH is reached. The number of drops
represents the amount of acid needed for the pool size as listed in the table.
Once familiar with the procedure the amount of acid for a desired change in pH
is easily estimated. Usually 100 to 300 ml (three to ten ounces) of acid will lower the
pH as required. It can be added directly to the pool water or diluted first. But is should
always be added slowly. Rapid addition of acid will reduce the alkalinity more and
change the pH less effectively.
Base Demand
There is a similar test and table for "base demand." This is rarely needed. In a
carefully maintained pool the water will never become too acidic. However, if there is
an accidental upset of the pH to values below 7 the base demand test may be useful.
See the section "Correcting Low pH."
CHLORINE CONCENTRATION
A good test kit will provide two tests for chlorine determination. One for "free
chlorine" and one for "total chlorine." The difference between them is the "combined
chlorine" level. Combined chlorine is produced when chlorine combines with waste
material to disinfect it. Chemically it is usually a chloramine. In a residential pool there
may be some combined chlorine if it has had heavy use but most of the time there will
be little or none. Periodic super-chlorination removes the combined chlorine.
The most important chlorine level cannot be directly tested. It is the effective
chlorine which is pH dependent. Unless both the free chlorine and the pH are in
range there is very little purifying or sanitizing.
Chlorine Measurements
Total chlorine is a measure of all the chlorine materials present in the pool
water. This includes hypochlorous acid, hypochlorite ion and chloramines. It does not
include chlorides (from salt or acid). It can be determined by the DPD or OTO method.
Free chlorine is a measure of hypochlorous acid and hypochlorite ion. It is
easiest to determine with the DPD method.
Combined chlorine is found by subtracting the free chlorine from the total
chlorine. It should be close to zero.
Effective chlorine is hypochlorous acid. It is pH dependent and is usually about
half of the free chlorine level.
CHLORINE TESTS AND MEASUREMENTS (Summary)
TOTAL chlorine (test) HOCl, OCl–, chloramines
FREE chlorine (test) HOCl, OCl–
COMBINED chlorine (calculated) chloramines (TOTAL – FREE)
EFFECTIVE chlorine HOCl (depends on pH)
Estimating Effective Chlorine (VERY IMPORTANT)
To estimate effective chlorine first measure the free chlorine with a DPD test.
Next reduce this amount by half to allow for the pH effect. If stabilizer is present (and
below 40 ppm) subtract another ten percent. If stabilizer is over 100 ppm effective
chlorine will be substantially reduced.
For example, if the free chlorine test reads 3 ppm then the effective level is 1.5
ppm (with the pH near 7.4). With CYA stabilizer at 30 ppm the effective chlorine is
further reduced to about 1.35 ppm.
In a second case if free chlorine were again 3 ppm but the pH was 7.6 with 100
ppm of stabilizer then the effective chlorine would be less than 0.5 ppm. In the first
example algae growth would be inhibited but not in the second, especially in hot
weather, even though the test results are the same.
Adjusting Chlorine
Liquid chlorine (sodium hypochlorite) can be added directly to the pool. Pour it
slowly along the perimeter for even distribution. Do not pour chlorine solution into the
skimmer -- it could corrode the filter.
Chlorine powder (calcium hypochlorite) can be added directly to the water
along the perimeter of the pool or cast over the surface. An alternate method
recommended by some manufacturers is to pre-dissolve the powder in a bucket and
pour the solution in the pool. Again, do not put this type of chlorine into the skimmer
(either the solid or a solution of it ) because it could corrode the filter.
Never toss tablets in the pool; they will corrode the cement. There are three
ways to handle them:
1.) They can be placed in the skimmer basket which causes them to dissolve faster.
This is only recommended if there are no metal parts in the pool plumbing.
2.) They can be added to a floating dispenser which allows them to dissolve slowly
and provides better distribution even when the pump is not running.
3.) There are in-line dispensers which can be connected to the piping of the water
circulation system. The tablets are added to a small tank and dissolve as pool
water is pumped through it. However, controlling the rate of addition is more
reliable with the floating device.
Hypochlorites (either solution or powder) last for a period of days whereas
tablets last for a period of weeks. With more frequent but smaller additions of either
type of chlorine the minimum amount remains at a higher, more effective level. This is
more cost effective but less convenient than using larger amounts less often.
It would be ideal to add small amounts continuously. In practice only the
chlorine and acid additions are critical since only the pH and chlorine concentration
can change rapidly. With hypochlorites (liquid or powder) more frequent correction of
pH is required -- daily additions of chlorine and acid will often be needed to maintain a
steady level of effective chlorine. With trichlor tablets (three-inch size) used in a
floating dispenser weekly addition is enough.
TOTAL ALKALINITY
Any material which takes up acid ions will contribute to total alkalinity.
Sometimes "total alkalinity" is referred to as "carbonate" alkalinity because it is the
bicarbonate concentration which is important. Since the pH determines the state of the
carbonate ion it will affect the test results; so pH has to be close to normal to get an
accurate result. (See the section on Carbonate Chemistry.)
The total alkalinity test should be performed at least every two weeks (once a
week in hot weather). When an addition of baking soda is needed it can be added
slowly into the skimmer. With the water circulating it will dissolve quickly.
The stabilizer compound (CYA) interferes with this test because it contributes to
alkalinity. About one third of it shows up. Typically this will add about ten ppm.
However, if the stabilizer is excessive (over 100 ppm) then it will contribute more than
30 ppm. It would be necessary to adjust for such a large interference since it is only
the bicarbonate which balances the water. When testing alkalinity remember to
reduce the "total" to estimate the bicarbonate content if stabilizer is present.
CALCIUM HARDNESS
The test for calcium is actually a water hardness test which also responds to
other minerals such as magnesium. This is not a problem for most pools since calcium
will predominate. However, in a hard water area the amount of the other minerals
present must be known in order to adjust for the interference. Public water utilities
should provide this information. A private well would have to be tested for minerals
other than calcium.
Calcium hardness should be tested every three months. Normally calcium will
drift to lower values and can be corrected with the addition of calcium chloride. If the
calcium level should go up unexpectedly the cement may be dissolving. Unless the
supply water is hard or a lot of calcium hypochlorite has been used there is a problem
with the water balance (alkalinity and pH). See the section on CALCIUM BALANCE.
STABILIZER CONCENTRATION
The test for cyanuric acid (CYA) is very important if a stabilized chlorine
compound is used. Continuous use of trichloro-s-triazinetrione (trichlor) causes the
level of stabilizer to increase. After three months the stabilizer content should be
determined. It is best to stay under 50 ppm. This is necessary to keep excessively
high levels from interfering with the chlorine activity or the determination of alkalinity.
This test is imprecise because it requires estimating the cloudiness (turbidity) of
the test solution. The easiest way to avoid excess is to limit the amount of stabilized
chlorine used for a season. There is no need for this test if neither stabilized chlorine
nor cyanuric acid is used, or if the amounts are limited.
TESTING CONDUCTIVITY
The conductivity of the pool water indicates the amount of dissolved solids in
the water, most of which is salt. The buffering and pH adjustments using bicarbonate
and acid cause salt to form. As the salt increases the conductivity increases.
This test can be done at a pool store; it is not critical. Once a year ask for a
determination of "total dissolved solids." Compare it with the tap water at the pool site.
When too high reduce it by draining some of the water and adding fresh water. (There
are some pools which use salt in the water for purification with automatic chlorinators.
In this case the conductivity should be higher than normal.)
TESTING SCHEDULES -- FREQUENCY
pH determination Almost daily
Chlorine concentration Several times a week
Total alkalinity Twice a month
Calcium hardness Four times a year
Stabilizer concentration Two to four times a year
Conductivity Once a year
/// *KEY POINTS* ABOUT TESTING \\\
1.) The amount of effective chlorine is the test kit measurement adjusted for pH and
the presence of stabilizer. It is lower than the test reading, usually by half.
2.) Accurate pH testing is essential to water maintenance based on chlorination.
3.) A complete test kit with a nomogram is the best choice to do your own
testing. It will put YOU in control of your pool.
/// SAMPLING THE WATER \\\
For meaningful results the water sample must represent the average condition
in the pool. For this reason the water should be circulating at least half an hour before
the sample is taken. Always use clean sampling containers and rinse them out after
each test. Do not discard the tested water into the pool.
If test results from samples taken at different locations are compared usually no
differences are found. Try this in your pool. If the results are different is may mean that
the circulation is not very effective. Check the outlets for the incoming water. Most can
be adjusted to change the direction of the water flow.
/// RECORD KEEPING \\\
A calendar is a convenient way to save test results. On a monthly calendar
each day's test results or chemical additions can be recorded in the appropriate space.
A notebook is useful for recording test results that are done less frequently such
as calcium and stabilizer levels. All the tests should be done together at least four
times a year. A record of these results is useful in developing an understanding of the
effects of the chemical additions.
/// CALCULATIONS \\\
Parts Per Million
Except for pH all other tests determine concentrations in "parts per million." It is
abbreviated as "ppm." It refers to the weight of the tested chemical compared to the
weight of the water in the pool.
The weight of water is 8.3 pounds per gallon. For a 15,000 gallon pool the
weight of the water is 8.3 times 15,000 which equals 124,500 pounds. Dividing this
weight by one million gives 0.1245 pounds. Therefore "one ppm" in a 15,000 gallon
pool is 0.1245 pounds which is about two ounces or 56 grams. If a 15,000 gallon pool
needed 20 ppm of a chemical then 20 times 0.1245 would be 2.5 pounds, the required
amount to add.
The chemical compounds are usually not 100% of the desired material so this
must also be taken into account. For example the different chlorine compounds are
different percentages of available chlorine.
It is not necessary to do these calculations each time an addition to the pool
water is required. Tables have been prepared for each of the chemical compounds of
interest. A large test kit will include a set of tables for determining the weight of the
chemical addition which will provide the desired increase in ppm for various pool
sizes.
Amount of Chemical Additions
The test results may indicate that certain additions are required to keep the pool
water in good balance. Using the tables from a test kit the amount of each addition
can be found for the size of the pool. Additions must be made one at a time and while
the pool water is circulating. Always allow time for one addition to disperse before
staring another. Always read the label and follow manufacturer's instructions before
adding a chemical to the pool.
After determining the amount of the addition it is always better to add only part
of it, especially if unsure of the pool capacity. Then the test can be run again and the
rest of the addition can be made as needed. Caution in making additions is always
advisable because it is easy to add more and impossible to remove over-additions.
The tables may give the addition amounts in either metric or standard
measures. A conversion table is given below for the amounts most commonly
encountered.
CONVERSION TABLE FOR LIQUID MEASURES
Milliliters (ml) Ounces (oz)
100 3.4
200 6.8
300 10.0
400 13.5
500 (half liter) 17.0 (about one pint)
1000 (one liter) 34.0 (about one quart)
3.785 liters (3785 ml) 128.0 (one gallon)
Pool Capacity
The size of a pool can be estimated in various ways. One way is to calculate
the volume based on the geometry. That is, multiply the average depth times the
surface area. For example, given a rectangular pool 18' x 36' with an average depth of
four feet the volume is 18 times 36 times 4 or about 2,600 cubic feet.
Once the volume is determined in cubic feet multiply by 62.3 pounds per cubic
foot for a pool capacity of 161,500 pounds. Dividing this by 8.3 pounds per gallon
gives 19,400 gallons. Or, combining the conversion factors, the volume in cubic feet
times 7.5 will give the pool capacity in gallons.
CONVERSION FACTORS FOR POOL CAPACITY
Pounds per gallon of water 8.3Pounds per cubic foot of water 62.3Gallons per cubic foot of water 7.5
For non-rectangular pools an estimate of the surface area is needed. One way
to do this is to draw on graph paper a scaled outline of the pool shape. Then count the
squares to estimate the area.
The easiest way to determine pool capacity is to check the water meter when
the pool is filled. This is the most accurate way to find the size in gallons. However,
there are not many occasions to do this.
A third method to estimate pool capacity is to note the effect of various size
additions on the increase in ppm. For example, if a ten pound addition of baking soda
gives only half the expected increase in ppm alkalinity then the pool capacity is
probably twice that expected. Additions of baking soda or calcium chloride can be
used to check on the estimated capacity.
/// PARTIAL DRAINING OF THE POOL \\\
Reasons to partially drain a pool are to reduce excessive stabilizer or dissolved
solids or to freshen the water. Over long periods dissolved organic material increases
especially if quaternary ammonium chlorides have been used.
Never completely empty a pool unless the ground water level has been
checked. If ground water is higher than the bottom of an empty pool it could lift out of
the ground. Many pools have a dry well underneath connected to a pipe used for
checking ground water and pumping it away.
/// OLD SCHOOL VS. NEW SCHOOL \\\
All of the above details about testing, adjusting and calculating additions of
chemicals are good things to know. But today many pool stores offer computer
analysis if you bring a water sample in. All you have to know is the temperature of the
pool and its capacity in gallons and the computer will do the analyses and calculate
the required additions. A word of caution: Not all store employees always know what
they are doing all the time. If you have doubts try bringing in samples of the same pool
water on different days or to different stores. There is always some variation in test
results because some of them are estimated or based on subjective judgments of color
or turbidity.
Obviously the sample water must be representative of the pool if the computer
aided analysis is to be meaningful. A clean sample container is a must and the
sample should be taken just prior to going to the store. Sometimes store employees
are too eager to recommend something be bought. You always have your own test kit
and the information provided in this manual to check on the recommendations. Again,
a good test kit with all the major tests is recommended for home use.
/// POOL WATER PROBLEMS \\\
Most problems will respond to shock treatment with liquid chlorine. It is an
inexpensive remedy worth trying before more drastic measures. Draining the pool,
refilling and balancing the water will take care of problems related only to the water.
For unusual problems involving equipment, the cement surface or the structure of the
pool seek the help of a professional pool service. company.
Algae
Even with regular preventive maintenance there can sometimes be algae
growth because chlorine levels are kept low for safety and economic reasons.
Chlorine and acid are the two items which deteriorate most rapidly. Weather
changes can hasten their disappearance. Since low chlorine or high pH results in
ineffective chlorination either can lead to algae growth. This is the most common
problem and is easy to solve. It is treated by super-chlorination or shock treatment as
described in the section CONTROL OF ALGAE.
Algae With High Chlorine
If chlorine is high and there is a lot of algae there could be two causes. The first
is high pH making the chlorine less effective. The second is too much cyanuric acid.
This condition, called "chlorine lock," makes super-chlorination or shock treatment less
effective. The cure is to lower the pH. If the algae persists, test the level of stabilizer --
if over 100 ppm partially drain the pool and add fresh water; if over 50 ppm do not use
stabilized chlorine for a few months.
Cloudy, Hazy Water
Cloudy water can have several causes. Among them are algae, high pH, high
alkalinity, high calcium, high combined chlorine or too much stabilizer or quaternary
ammonium chloride. Inert or inactive ingredients in solid chlorinating compounds can
cause cloudiness unless the filtering system removes them. Calcium hypochlorite can
cause temporary cloudiness. A tear in the filter will create cloudy water, especially if
diatomaceous earth is used.
To cure cloudy water first adjust the pH to 7.2 to 7.4. If cloudiness persists
check the filter pressure and clean the filter or change the DE. Check the filter for
holes if the DE appears to be leaking into the pool. Next super-chlorinate or shock
treat as required.
Also be sure the water is balanced with respect to calcium, carbonate and pH
for the given temperature. Cloudiness could occur during hot weather when rising
water temperature causes calcium carbonate to precipitate.
If the water is still cloudy it may be caused by small particles which pass through
the filter. These are suspended solids. The use of a flocculent (sequestrant) may be
required. This is a material which will cause suspended particles to clump together so
that the filter can remove them. A pool supply store will have one or more brands to
choose from.
Colored Water
Swimming pool water should be blue. When it appears to be a different color
there are two common causes. The first is algae which is discussed above. Algae
usually colors water green. The second is contamination with metal ions. This is an
infrequent problem. The color can vary depending on the metal which is present. Iron
and copper are the most common.
A first attempt to eliminate colored water should be to shock treat with chlorine
solution. If this is ineffective then a treatment to remove metal ions should be tried
next. Pool supply stores have products that will remove metal ions. Before treatment
have the water analyzed to identify the contaminant.
Foaming
Foaming is a problem that is usually caused by the over use of quaternary
ammonium chlorides. Waiting for the excess to dissipate is probably the best solution;
otherwise, it will be necessary to partially drain and refill with fresh water.
If foaming is caused by the presence of materials which do not belong in the
pool (like detergents) then it will be necessary to drain the pool to remove them.
Odors
If there is an unpleasant or strong odor from the pool water it is most likely from
the formation chloramines. This can be treated by chlorine shock which will eliminate
the combined chlorine. Chlorine treated water has a slight smell of chlorine. A strong
smell is often caused by urine, an amine, in the pool water combining with the chlorine
to form a chloramine.
High Dissolved Solids
This is a condition that will occur eventually. A side effect of buffering with
baking soda and acid is the formation of salt. The salt and other water treatment
compounds continue to accumulate in the pool water. It can be several years before
they become objectionable. The only way to reduce them is to partially drain the pool
and add fresh water. Flocculents will not eliminate dissolved solids.
High Filter Pressure
A sudden increase in filter pressure might be caused by an increase in pH
especially in hot weather. Precipitating calcium carbonate could plug the filter. Treat
this problem by adjusting the pH and cleaning the filter.
Rough Deposits On Pool Surfaces
If white crystalline deposits form on the cement surfaces it is usually caused by
high pH especially in hot weather. The high water temperature in combination with
high pH causes calcium to precipitate. The deposits usually scrape off easily and
when the pH is adjusted below 7.4 will dissolve.
In some cases the calcium content may have become too high. Stop using any
material which contains calcium. Adjust the pH and alkalinity to balance the calcium at
the present water temperature. In severe cases partially drain the pool and refill to
remove some of the calcium.
Cement Erosion
Cement erosion occurs if calcium dissolves from the cement. Neglecting it can
be very expensive. Its cause and cure are discussed below in the section on big
problems.
Staining of Cement
If a stain appears, which is a discoloration that does not brush off, it can usually
be removed by adding chlorine right near the spot. At the bottom of the pool this can
be done by placing one end of a pole near the stain and pouring liquid chlorine down
the other end. Follow it with a few cups of pool water to flush the heavier chlorine
solution out at the end of the pole near the stain. If you are not agile enough to do this
get someone else to help in order to avoid spilling chlorine on yourself. Do this with
the circulation turned off so that the water is still and leave it that way for a while.
Stains will often bleach out within a few minutes. Later on circulate the water and
adjust the pH if necessary in the usual way with an acid addition.
For intractable stains the advice of a pool professional may be necessary. He
may want to do tests to determine if there is something in the water such as metal ions
which should not be there.
/// HOW TO AVOID BIG PROBLEMS \\\
A pool with properly balanced water should last for a very long time -- at least
several decades. However, out of balance water can cause significant damage after
long exposure (about two years). The surface of the pool becomes pitted and rough.
The white finish cement may crumble and erode in patches down to the rough cement
below it. At this stage the calcium level may increase even though calcium is not
added. To repair such damage the pool is drained, resurfaced and refilled at a cost of
thousands of dollars.
Water can be out of balance when regular testing is not done for pH, alkalinity,
calcium and stabilizer. However, even with regular testing a situation can occur where
the water appears to be balanced but is not. The use of stabilized chlorine increases
the amount of cyanuric acid in the pool. This influences the alkalinity test. This
situation causes the pool water to appear balanced when in fact the carbon alkalinity
is actually very low. Total alkalinity will reflect the high stabilizer content and appear to
be normal. Unless this is recognized the water will become corrosive to the cement.
If water is left out of balance when refilling a pool it can cause serious problems
depending on the chemistry of the incoming water. See the section on "Incoming
Water Supply." A high pH may cause precipitation and staining of the cement if it is not
promptly adjusted.
To avoid these problems remember that:
1.) High levels of CYA stabilizer can result from continuous use of stabilized
chlorine (trichlor).
2.) The total alkalinity measurement has to be corrected if the stabilizer content is
high in order to know the true level of carbonate alkalinity.
3.) It is important to control water balance even when filling a pool.
/// ACHIEVING BALANCED POOL WATER \\\
The next two sections provide an overall view of how to put all the preceding
information together to achieve and maintain balanced pool water. To check the water
balance of a pool there are three major steps:
STEP ONE: Mechanical and Visual Inspection
1.) Make sure that the pump is operating.
2.) Check the flow rate of the water coming out of the return lines to the pool. Put
your hand in front of the water inlets to feel the force and direction of the water.
Redirect the water inlet jets as necessary for maximum circulation.
3.) Check the pressure of the filtering unit and compare it to the manufacturer's
recommended range. It may need cleaning.
4.) Look at the color and clarity. The water should be clear and blue -- deeper blue
at the deep end.
5.) Look for algae along the tile and on the walls and floor of the pool. It can
appear as a yellowish powder, dark green slime, or black spots.
5a.) If there is little or no algae omit STEP TWO and go to STEP
THREE and test the water.
5b.) Super-chlorinate if there is a small amount of algae. See the
section on CONTROL OF ALGAE.
5c.) For large amounts of algae use a shock treatment as described
below in STEP TWO.
STEP TWO: Shock Treatment (Only if required)
Add liquid chlorine to provide 30 to 60 ppm chlorine. This will be 5 to 10
gallons of ten percent liquid chlorine for a 15,000 gallon pool.
Run the pump and filter continuously until the water clears. This could take
several days and require cleaning the filter several times.
If this is your first experience with a pool it may be best to consult a pool care
service company if you are faced with very contaminated water.
After any required fixes to the equipment and brushing, filtering and vacuuming
and shock treatment with chlorine there are three questions to complete a visual
inspection: Is the water blue? Is it clear? Is it clean? When the water is blue, clear
and free of dirt or debris it is time to check for the things you can't see using the
chemical tests. It should also be odor free.
STEP THREE: Chemical Testing of the Water
1.) Sample the water and perform the tests for chlorine, pH, alkalinity, calcium and
stabilizer.
2.) Measure the water temperature.
3.) Compare the test results for all five tests to the ideal values.
4.) Make sure that the amount of cyanuric acid will not cause problems -- it should
be less than 40 ppm. If it is close to acceptable there is no need to adjust it
immediately. If it is over 100 ppm it will be necessary to partially drain the pool
and refill.
5a.) If calcium is below 200 ppm bring it to 300 ppm by adding calcium chloride.
5b.) If calcium is over 400 ppm use a nomogram or table to determine the
appropriate pH and alkalinity. Do not use the values given below.
6.) Adjust the chlorine concentration to about two ppm if it is low.
7.) Adjust the total alkalinity to about 90 ppm.
8.) Adjust the pH after making all the other adjustments. Keep it above 7.0 and
below 7.6 aiming for approximately 7.4.
The section on TESTING AND ADJUSTING POOL WATER contains useful
details for carrying out the above procedure. The test kit will contain the necessary
tables to find the amounts of the additions to bring the calcium, chlorine, alkalinity and
pH to the desired values in this order.
The sections on CALCIUM BALANCE and IDEAL CONDITIONS will provide
background information about balancing the chemicals for the water temperature.
The section on CHLORINATION provides descriptions of the various types of
chlorine compounds available. The choice will depend on the season, the calcium
hardness and the amount of stabilizer present.
/// MAINTAINING BALANCED POOL WATER \\\
Maintaining the chemical balance in pool water is a matter of making
adjustments for the decomposition of some of the chemicals and for seasonal changes
in temperature. There are many ways to accomplish this. The method described
below was selected for economy and convenience.
With proper filtration and with the water balanced with respect to pH, chlorine,
alkalinity, calcium and stabilizer the following procedures will then maintain the
balance.
Summer Procedures
1.) Use trichlor tablets for the four hottest months of the year. This will make it
easier to keep the chlorine level uniform and the pH stable. It will also provide
cyanuric acid (CYA) stabilizer during the season when the sunlight is most intense.
The three-inch tablet size is recommended for use with a floating dispenser to
provide the most reliable release rate of chlorine. From one to three tablets per week
should be used in a fifteen thousand gallon pool This is approximately forty to fifty
tablets per year (twenty pounds). A few can be reserved for use in midwinter to boost
the stabilizer level but the major portion will be required in the summer.
2.) When the chlorine requirements are not met by the trichlor tablets (at the
maximum rate of one tablet per 5,000 gallons per week) then use chlorine solution to
supplement the tablets.
3.) During the hottest season keep the pH around 7.3 and the carbonate alkalinity
around 80 ppm. Muriatic acid will be used to adjust the pH and baking soda will be
used to add carbonate alkalinity.
4.) Calcium should be kept near 300 ppm.
5.) After heavy use or rain or if algae is present super-chlorinate with liquid chlorine
by adding an additional 3 to 5 ppm over the usual level. If algae gets out of hand
shock treat with a large dose of liquid chlorine to obtain ten or more ppm.
6.) If there is algae on the tile chlorine solution can be poured along the perimeter
when the water is still and left overnight for maximum effect.
7.) If algae occurs on the bottom of the pool calcium hypochlorite powder can be
cast over the surface when the water is still and left overnight.
Off-Season Procedures
1.) During the cooler season it will be easier to maintain the water purity. In order
to allow the stabilizer concentration to drop use liquid chlorine only.
2.) This will require more frequent adjusting of the pH with acid. The pH can be
kept at about 7.5 and the carbonate alkalinity can be kept at about 100 ppm.
Off-Season Time Saver
For pools which remain open but unused during the winter there is a procedure
which will reduce some of the maintenance effort. If using chlorine solution change
the addition schedule as follows:
1.) Instead of one pint daily add about three quarts weekly.
2.) Adjust the pH to 7.4 with acid.
This is once-a-week super-chlorination. Select the amount so that at least one
ppm chlorine remains a week later. There will be a higher than necessary chlorine
level most of the time.
Testing for chlorine and pH can also be reduced to once a week. This time-
saving procedure replaces daily maintenance with testing and additions which can be
carried out on a weekend.
Preventive Maintenance for Away Time
During a period of time when regular maintenance will not be possible, such as
a trip away from home, preventive shock treatment will delay the onset of algae
growth. If the pool is to be unused keeping the chlorine at a higher than normal level
will prevent problems until regular maintenance can be resumed.
/// QUARTERLY TESTING TO MAINTAIN A BALANCED POOL \\\
The key to maintaining pool water is regular testing. And at least four times a
year all five chemical tests should be performed together. The cyanuric acid test can
be eliminated if the use of stabilized chlorine is limited. Be careful about choosing a
small test kit for just chlorine and pH. Some of them are either not reliable or difficult to
read precisely enough. Wrong information is just as bad as no information. There are
a few large test kits which are expensive but they contain everything you need to do a
complete analysis of your pool water. One of the best is "tailor made" for your pool.
This is the only brand name hint I've used. Try an internet search for test kits for pool
water and you will find them.
/// SEASONAL CHECK LIST \\\
Beginning of the Season, Opening the Pool:
1.) Clean the filter system.
2.) Shock treat.
3.) Test the calcium level and bring it to about 300 ppm.
4.) Check the level of stabilizer. It should be about 20 to 40 ppm.
5.) Test and adjust alkalinity and chlorine levels.
6.) Test and adjust the pH.
7.) Start using three-inch tablets of trichlor.
Summer:
1.) Increase the filtering/circulating time. See the section on "Pump Schedule" in
FILTERING.
2.) Use the trichlor tablets approximately one per week per 5,000 gallons.
3.) Use liquid chlorine for super-chlorination approximately once per week.
4.) Use powder chlorine for spot algae, only if necessary.
Off-Season:
1.) Reduce the filtering /circulating time or close the pool.
2.) Use weekly super-chlorination with liquid chlorine to reduce maintenance time.
/// CHEMICAL SUPPLIES \\\
The chemical supplies needed for the chlorination methods recommended in
this manual are listed below.
1.) Trichlor tablets Trichloro-s-triazinetrione, three-inch tablets, 99%
2.) Liquid chlorine Sodium hypochlorite, NaOCl, ten percent solution
3.) Muriatic acid Hydrochloric acid, HCl, 31.5%, concentrated, 20º Baume
4.) Baking soda Sodium bicarbonate, NaHCO3
5.) Calcium chloride Calcium dichloride dihydrate,CaCl2.2H2O, 80% (flakes) or 94% (pellets)
Four of them are needed on a regular basis: the tablets, liquid chlorine, acid
and baking soda. Item (5.) is not needed in hard water areas at all and for normal
water areas could be bought as needed since it is only used a few times a year.
Nothing else is required for normal maintenance based on chlorination.
I have not used brand names because it is the chemicals and their purity that is
important. Quite often they will be coming from the same manufacturing plant with
different packaging.
/// *KEY POINTS* ABOUT MAINTAINING POOL WATER \\\
1.) Liquid chlorine (sodium hypochlorite solution) is the most cost effective way to
chlorinate a pool.
2.) Trichlor tablets should be used for three or four months in summer. They
provide chlorination and cyanuric acid stabilizer.
3.) Cyanuric acid stabilizer should be kept around 50 ppm by limiting the amount of
trichlor used.
4.) The cement is preserved by balancing calcium and carbonate levels relative to
the water temperature and pH.
5.) Calcium chloride additions may be needed to keep calcium levels near 300
ppm.
6.) Total alkalinity should be about 90 ppm. The usual range is 70 to 130 and the
optimum depends on the water temperature.
7.) The optimum pH is 7.4 and is the single most important factor to control.
8.) Control of pH is achieved with hydrochloric (muriatic) acid and baking soda
(sodium bicarbonate).
9.) Algae can be controlled by manual brushing and periodic super-chlorination or
occasional shock treatment with chlorine solution.
10.) The best spot algaecide is calcium hypochlorite powder.
11.) A comprehensive test kit is necessary for maintaining balanced pool water.
Chemical adjustments based on regular testing will eliminate most problems.
12.) When purchasing supplies pay for the chemical compounds and not for brand
names. Check the labels for ingredients and the percent active. See the lists
for the necessary chemicals and price comparisons.
/// EQUIPMENT CHECK LIST \\\
* Calendar or Notebook
* Pool thermometer
* Floating dispenser for solid chlorine tablets.
* Adjustable length pole with pool brush, skimming net, vacuum head and hose.
* Hand brush with plastic or stainless steel bristles for cleaning the tile.
* Plastic one quart measuring cup with metric calibrations.
* Storage locker for chemicals.
* Petroleum jelly or silicone lubricant for O-rings.
* Water sample bottle for store analysis.
* Test kit for pH, chlorine, alkalinity, calcium and stabilizer including tables for
additions and a nomogram for water balance.
/// FILTERING \\\
Filtration and circulation are essential to good water maintenance. Algae and
debris are removed and the growth of algae is inhibited.
Cartridge Filters
Cartridge filters are commonly used in residential swimming pools to remove
solid debris from the water. As the cartridge picks up solid materials its effective pore
size becomes smaller. This results in higher pressure and decreased flow. When this
happens the pump must run longer to filter the same volume of water. The decreased
flow reduces the circulation in the pool and when it is too low the cartridge must be
removed and cleaned.
The usual routine for cleaning a cartridge filter is to take it apart and hose it
down. The same cartridge is then replaced in the filter housing and used again for
another cycle. The advantage of cartridge filters is the initial lower cost of the
equipment. The disadvantages are the inconvenience of the cleaning procedure and
eventual replacement cost of the cartridge element.
DE Filters
Diatomaceous earth (DE) filters are more effective than cartridge filters. The
result is cleaner water which looks much clearer.
These filters pull water through a fine powder suspended on a fabric. When the
filter pressure goes up the flow decreases and the powder has to be replaced with
fresh DE. For DE filters with a multi-port valve this procedure is quick and easy. The
used powder is blown off the fabric with pool water by setting the valve position to
"backwash." New DE powder is added through the skimmer with the valve in the
normal "filter" position.
At least once a year the filter element should be removed from the housing and
hosed down. This can be very easily done on a model with a clamp and O-ring seal
securing the cover.
The disadvantage of DE filters is higher initial cost. However, in the long run
they are cheaper than cartridge filters because the DE powder is inexpensive. (Note:
Sand filters are somewhere in between cartridge and DE filters in effectiveness and
cost.)
Pump Schedule
Filtering and circulating constantly would be best for the water quality but would
cost more and wear out the equipment sooner, especially the pump motor. As usual
there is a trade-off between cost, convenience and necessity. Less effective filtering
systems may have to run almost all day. A more expensive over-sized system will
allow for shorter running times and save a substantial amount of electricity. A timer is
essential for convenient scheduling. By alternating on and off periods the motor has a
chance to cool down and electricity can be saved without reducing the effectiveness.
Water temperature and amount of pool use need to be considered. When the
water temperature is above 85º F more filtering is needed than when it is below 60º F.
During the winter if the pool water is very cold very little circulation and filtration is
required and the pump can be scheduled to run for a few hours per day. Pools in a
cold winter climate do not need to be filtered until they are reopened.
/// BRUSHING AND VACUUMING \\\
Unless there is an automatic cleaner the sides and bottom of the pool should be
brushed occasionally. Use a pool brush with an adjustable telescopic pole. This will
dislodge debris which does not float. It also helps to prevent algae growth. Brushing
is more effective for removing algae than vacuuming. If there is algae to be removed
brush first to dislodge it and vacuum last. Brush debris toward the main drain. For
better suction at the drain during brushing close the skimmer line.
For debris which floats a hand held net can be used. A small hand brush is
needed to brush the tile and grout. For the spaces between tiles a toothbrush is very
effective.
A manual pool vacuum attachment connects to the skimmer outlet with a flexible
hose. It is used to remove debris which has sunk to the bottom of the pool. For
increased suction close down the main drain while vacuuming. Vacuum as required;
this will vary considerably depending on the pool location and enclosure. This chore
can be handled with an automatic cleaner. Automatic cleaners require maintenance
and cleaning themselves, so there is a trade-off here, not a completely hands-free
solution.
/// SKIMMER \\\
The simmer collects floating debris from the surface of the water. It does this by
pulling water over the edge of a floating weir and through a basket. (Some pools have
a fixed weir.)
The floating weir is the smaller upper part of the skimmer. It is designed so that
it will adjust to changes in water level. Once in a while a floating weir may become
stuck which causes air to be sucked into the pump. Simply dislodge the weir so that it
floats again. This is the reason for maintaining the water level at the midpoint of the
tile.
The floating weir usually has a pocket under its rim which has to be cleaned out
occasionally. The bottom section of the skimmer (the basket) should be periodically
removed and emptied. A screened-in pool will have less floating debris but an open
outdoor pools may have an occasional frog or mouse to remove. A daily check at least
is suggested in this case.
/// PUMP TRAP \\\
Most pumps for residential swimming pools have a trap to remove debris just
before the water enters the pump. This trap usually has a see-through cover. At least
every few weeks the cover should be removed when the pump is off to clean out the
basket inside. The frequency depends on whether a pool is screened-in or not. The
number of trees in the area also affects how much solid matter ends up in the trap
basket.
The cover to the trap filter should be replaced hand tight. It is a good idea to
lubricate the O-ring with petroleum jelly. A home-made wrench is very useful for
loosening the cover. The wrench can be made from a piece of 2"x6" lumber with a
notch cut in it to fit over the cover handle. Never use the wrench to tighten the cover to
avoid deforming the O-ring.
/// SAFETY \\\
The following reminders about the safe handling of pool chemicals should
always be observed.
* Always follow the manufacturer's instructions.
* Always read the label before use.
* Only add chemicals intended for swimming pools.
* Store pool chemicals in a secure place (child-proof).
* Never mix different chemicals together.
* Wait until one chemical addition is complete and has dispersed before making another.
* Dispose of empty containers after rinsing out with pool water. This puts all the material into the pool and keeps the trash barrel safe.
* Observe the precautions necessary for each type of chemical. Avoid skin contact, do not breathe the dust or fumes. Use rubber gloves, goggles or a dust mask as appropriate.
* Never add hazardous chemicals when the pool is in use.
* Do not use the pool until hazardous chemical additions have been dispersed.
Risks of Swimming In Chlorinated Water
Water has been chlorinated for drinking since the turn of the century. Generally
chlorine gas or liquid chlorine has been used. This results in the formation of
hypochlorous acid and hypochlorite ion as described in the section on
CHLORINATION. Studies of chlorinated drinking water have concluded the benefits
far exceed the risks.
With regard to swimming in chlorinated water there are several points to keep in
mind:
1.) The level of chlorine in swimming pools is about the same as, but can be higher
than, drinking water -- but not much higher when swimming is allowed.
2.) Swimming pool water is not intended to be ingested.
3.) The health consequences of not disinfecting water can be far more serious than
chlorine exposure.
4.) The use of chlorinated water in swimming pools has a long history -- about one
hundred years. No other method of water purification has been subjected to the
scrutiny that chlorination has or has been used on as wide a scale or for as long
a time.
Recently it has been learned that when water is chlorinated there may also be
traces of organochlorine compounds formed. Some of these are known to be
carcinogens (cause cancer). In spite of this the studies continue to find that drinking
chlorinated water is an acceptable risk.
As a practical matter when chlorinating swimming pool water the level of
chlorine should be kept as low as possible to avoid exposure risks. This also keeps
the cost lower. However, if the amount of chlorine is not sufficient then bacteria and
algae will flourish which is a health hazard. The cost of eliminating algae blooms and
excess bacteria is greater than the cost of routinely controlling them.
Safety and economics both argue for using a minimum level of chlorine. Small
and frequent additions of chlorinating compounds are less convenient but safer and
more economical. If a pool is not in use it is convenient to increase the chlorine level
with larger but less frequent additions of chlorine. See the section on "Adjusting
Chlorine" in TESTING AND ADJUSTING POOL WATER.
/// COST ANALYSIS \\\
When the methods described in this manual are used the amounts of chemical
supplies for maintaining 15,000 gallons for one year are approximately:
1.) Chlorine tablets: About 45 to 50 tablets (twenty-five pounds). This amount of
stabilized chlorine will provide chlorination for about five months and enough
stabilizer for one year.
2.) Chlorine solution: About 10 to 12 gallons per year to supplement the tablets
and for super-chlorination. And about seven gallons for shock, if needed.
3.) Calcium chloride: The amount will depend on the "hardness" of the water
supply. For soft water areas about 25 to 50 pounds per year should maintain
calcium at about 300 ppm.
4.) Hydrochloric (Muriatic) acid: About ten gallons per year to adjust the pH.
5.) Baking soda: About fifty pounds per year to adjust the alkalinity.
Notes on other optional materials:
Chlorine powder: About 12 pounds per year could be used as a spot algaecide
and for super-chlorination or shock, but only as an option, otherwise use another
seven gallons of liquid chlorine.
Algaecide: No additional algaecides should be required. The three forms of
chlorine listed above will take care of routine chlorination and super-chlorination and
shock treatments. See CONTROL OF ALGAE, Cost Comparison section.
Purchasing Chemical Supplies
See the two page chart PRICE COMPARISONS OF POOL CHEMICALS. The
relative prices for supplies are given. The actual dollar prices will vary depending on
the area. Note that the prices have been adjusted for the amount of active material. It
is important to check both the ingredients and the percent active material.
Buying in bulk or buying non-branded materials will reduce costs. This is
especially true for baking soda and calcium chloride flakes. The price of some
chlorine compounds is more sensitive to quantity than others. Calcium hypochlorite
(dry chlorine) will be much cheaper in drums. Packaging also affects price so single
pound packs cost less than pails on a per pound basis.
The chemical effectiveness is important in some cases. Dry acid is not only
more expensive but it is less effective so more of it must be purchased to replace a
given weight of muriatic ace. One major money saving strategy is to use liquid
chlorine for super-chlorination and shock treatment to prevent algae growth. The cost
of exotic algaecides is often $50 per gallon; this is why they are usually sold by the
pint or quart.
Some treatments for algae are just small packages of the usual chlorinating
compounds disguised with clever brand names. A gallon of liquid chlorine will out
perform them at a fraction of the cost.
Costs of Testing
The cost of testing will average $15 per year. A complete test kit costs about
$65 and will last for several years. Replacing reagents will cost about $20 to $25 per
year.
Summary of Estimated Annual Costs (for a 15,000 gallon pool)
Chlorine tablets $60 to 80
Chlorine solution $70 to 100
Acid $ 50 to 75
Baking soda $ 30 to 50
Calcium flakes $ 0 to 30
Test kit supplies $ 20 to 30
YEAR'S TOTAL $ 230 to 365
These costs are estimated for an area where there is competition among
suppliers and they include sales taxes of seven percent. Your costs may be lower but
should not have to be higher than these unless you are in an area where pool
supplies are not commodity items.
This is about $15 per thousand gallons per year. A ten thousand gallon pool
would cost about $150 per year to maintain and a twenty thousand gallon pool should
cost about $300 per year.
PRICE COMPARISONS OF POOL CHEMICALS -- CHLORINE COMPOUNDS
Chlorine compound: Relative Prices Per Pound, Active:
Sodium hypochlorite
2.5 gallon bulk solution 1.00
one gallon prepackaged 1.70
Trichlor tablets * 2.50
Calcium hypochlorite **
envelopes 1.50
pail 3.00
drum 1.75
Lithium hypochlorite 20.00
Dichloro-s-triazinetrione 4.50
Notes:* Trichlor requires less acid for pH adjustment and it includes stabilizer (cyanuric
acid) which offsets the price compared to other sources of chlorination.
** Calcium hypochlorite chlorinates and provides calcium so less calcium chloride will be required.
PRICE COMPARISON OF POOL CHEMICALS -- OTHERS
Relative Prices Per Pound of Active Material
Compounds for pH control:
Muriatic acid (HCl) 0.50
Sodium bisulfate (Dry acid) # 0.95
Sodium bicarbonate (baking soda), bulk 0.35
Sodium bicarbonate, small package 1.00
Sodium carbonate (soda ash) ## 0.80
Other compounds:
Calcium chloride, unbranded, bulk 0.50
Calcium chloride, specialty brand 1.15
Quaternary ammonium chlorides 4.50
Cyanuric acid (stabilizer) 2.25
Notes:# Dry acid is less effective on a weight basis by a factor of three making muriatic acid five times more cost effective.
## Baking soda provides more carbonate on a weight basis than soda ash so it is a more effective buffering agent. This increases its price advantage. However, for acid absorption to raise pH, soda ash is more effective but not enough to offset the higher price.
POOL CHEMICAL DATA SHEET
Name(s): Sodium hypochloriteChlorine solutionLiquid chlorineNaOCl
Type of Compound: Chlorine source, liquid
Description: Ten percent solution in waterYellowish liquid, similar to bleachIrritant -- avoid contactOxidizerCorrosive -- handle with cautionLimited shelf life
POOL USE:Source of chlorine (hypochlorous acid) for routine chlorination, super-chlorination and shock treatment.The most cost effective algaecide available.Causes pH to increase.
Caution: Liquid chlorine is corrosive and must be handled with care.
Alternate: Calcium hypochlorite
RECOMMENDATION: Sodium hypochlorite is recommended as the most cost
effective source of chlorine.
POOL CHEMICAL DATA SHEET
Name(s): Trichloro-s-triazinetrioneTrichlorChlorine tabletsTrichloroisocyanuric acid
Type of Compound: Chlorine source, solid, contains stabilizer (cyanuric acid)
Description: Tablets, three-inch diameter, white Also in smaller tablet sizes, sticks and granules99% active, 89% available chlorine
POOL USE:Source of chlorine (hypochlorous acid) for routine chlorination and super-chlorination.Source of stabilizer (cyanuric acid).Does not upset pH.
Caution: Continuous use of trichlor can result in excessive build-up of CYA stabilizer.
Alternate: Sodium hypochlorite solution and cyanuric acid crystals.
RECOMMENDATION: Trichlor three-inch tablets are recommended as a cost effective
source of chlorine and stabilizer.
POOL CHEMICAL DATA SHEET
Name(s): Calcium hypochloriteDry chlorineChlorine powderGranular chlorineCa(OCl)2 or Ca (ClO)2
Type of Compound: Chlorine source, solid, contains calcium
Description: White solidGranules, powder, tablets or cartridgesOxidizerIrritant -- avoid contact65% active, 35% inert (sometimes 75/25)65% available chlorine
POOL USE:Source of chlorine (hypochlorous acid) for routine chlorination, super-chlorination and shock treatment.An effective algaecide.An excellent spot algaecide.Causes pH to increase.Also provides calcium.A solid alternative to liquid chlorine for easier handling.
Caution: Should not be used in pools with hard water problems. Continuous use will add about 250 ppm calcium per year.
Caution: The inert material may give the water a cloudy appearance until it is removed by filtering.
Alternate: Sodium hypochlorite
POOL CHEMICAL DATA SHEET
Name(s): Lithium hypochloriteLi (OCl) or Li (ClO)
Type of Compound: Chlorine source, solid
Description: White powderOxidizerIrritant -- avoid contact, do not breathe the dust70% inert
POOL USE:Source of chlorine (hypochlorous acid) for routine chlorination, super-chlorination or shock treatment.Causes pH to increase.Does not add calcium or stabilizer.Easier to handle than liquid chlorine.An expensive alternative source of chlorine.
Alternate: Sodium hypochlorite
POOL CHEMICAL DATA SHEET
Name(s): Sodium dichloro-s-triazinetrione dihydrateDichlor
Type of Compound: Chlorine source, solid, contains stabilizer (cyanuric acid)
Description: White granules99% activeIrritating -- avoid breathing the dustOxidizer
POOL USE:Source of chlorine (hypochlorous acid) for routine chlorination, super-chlorination or shock treatment.Source of stabilizer (cyanuric acid)
Caution: Should not be used if cyanuric acid levels are high.
Alternate: Trichloro-s-triazinetrione
NOT RECOMMENDED because it contains less chlorine and more stabilizer than
trichlor.
POOL CHEMICAL DATA SHEET
Name(s): Hydrochloric acidMuriatic acidHCl
Type of Compound: For control of pH. It lowers pH.
Description: Solution of acid in water, concentrated, 20º Baume, 31.5%Corrosive -- avoid contactIrritating -- avoid breathing fumes
POOL USE:Lowers pH.
Caution: Acid solution is corrosive and must be handled with care.
Alternate: Sodium bisulfate
RECOMMENDATION:
Hydrochloric (muriatic) acid is recommended as a cost effective method for
lowering pH. It is five times more cost effective than sodium bisulfate.
POOL CHEMICAL DATA SHEET
Name(s): Sodium bisulfateDry acidSodium hydrogen sulfateSodium bisulfate mono-hydrateNaHSO4
Type of Compound: For control of pH. It lowers pH.
Description: White powderCorrosive -- avoid contactHygroscopic -- absorbs moisture
POOL USE:Lowers pH.A solid alternative to liquid acid easier to handle and store.
Alternate: Hydrochloric acid (muriatic acid)
POOL CHEMICAL DATA SHEET
Name(s): Sodium bicarbonateBaking sodaSodium hydrogen carbonateNaHCO3
Type of Compound: For control of pH. It raises the pH. For buffering. It stabilizes the pH. Source of carbonate ions for cement stability.
Description: White powder. Other uses include cooking, cleaning, deodorizing and medication as an antacid.
POOL USE:Baking soda slows down changes in pH.It also prevents the cement from dissolving.It can be used to adjust pH to higher, more basic values.
RECOMMENDATIONS:Baking soda is recommended as a cost effective source of carbonate to buffer the pH and preserve the cement.
Alternate: Sodium carbonate (soda ash)
POOL CHEMICAL DATA SHEET
Name(s): Sodium carbonateSoda ashSodium sesquicarbonateNa2CO3 or Na2.NaHCO3.2H2O
Type of Compound: For control of pH. It raises pH. A source of carbonate ions for cement stability.
Description: White powder, granular
POOL USE:It can be used to raise pH. It is useful when the pH is very low.It can be used to raise carbonate alkalinity. However, the percentage by weight of carbonate is greater in baking soda.
Alternate: Baking soda (sodium bicarbonate)
POOL CHEMICAL DATA SHEET
Name(s): Calcium chlorideCalcium dichlorideCalcium dichloride dihydrateCaCl2.2H2O
Type of Compound: Calcium source
Description: Solid, white, flakes or pelletsHygroscopic -- absorbs moistureIrritant -- avoid contact80% calcium chloride plus 20% other chlorides; can be up to 94% Ca
POOL USE:A source of calcium to balance the solubility of the calcium in the cement.
Caution: Too much calcium will result in rough deposits on the pool surfaces.
Caution: Too little calcium will allow the cement to dissolve.
RECOMMENDATION: Bulk calcium chloride is recommended as a cost effective
source of calcium.
POOL CHEMICAL DATA SHEET
Name(s): Quaternary alkyl ammonium chloridesUsually a mixture of several compounds within this chemical family.For example: n-alkyl dimethyl benzyl ammonium chloride
n-alkyl dimethyl ethylbenzyl ammonium chloride
Type of Compound: Algaecide
Description: Ten percent solution in water
POOL USE:
An effective algaecide chemically different from chlorination.An optional routine treatment for inhibition of algae growth.
Caution: Too much quaternary ammonium chlorides will cause foaming.
Not recommended.
POOL CHEMICAL DATA SHEET
Name(s): Cyanuric acidCYAStabilizerWater conditioner1,3,5-triazine-2,4,6--triol
Type of Compound: Chlorine stabilizer
Description: Solid, white, flakes or granulesIrritant -- avoid contactHygroscopic -- absorbs moisture
POOL USE:Cyanuric acid at 20 to 40 ppm extends the lifetime and effectiveness of chlorine by protecting it from degradation by the ultra-violet rays of the sun.
Caution: Too much cyanuric acid will inhibit the effectiveness of chlorine.
Caution: Too much cyanuric acid will mask a deficiency in carbonate alkalinity by increasing the total alkalinity.
Alternate: Stabilized chlorine (trichloro-s-triazinetrione)
SUMMARY OF POOL CHEMICALS AND RECOMMENDED USES
Sodium hypochlorite Recommended for chlorination, super-chlorination and shock treatment.
Trichloro-s-triazinetrione Recommended for chlorination and as a source of stabilizer.
Calcium hypochlorite Alternate source of chlorine and calcium. Recommended as a spot algaecide.
Lithium hypochlorite Alternate source of chlorine. Expensive.
Sodium dichloro-s- Not recommended for routine use.triazinetrione
Hydrochloric acid Recommended for lowering pH.(Muriatic acid)
Sodium bisulfate Alternate for lowering pH.(Dry acid)
Sodium bicarbonate Recommended for buffering pH and as a source of (Baking soda) carbonate.
Sodium carbonate Alternate source of carbonate. Can be used if(Soda ash) large increases in pH are needed.
Calcium chloride Recommended source of calcium.
Alkyl ammonium chlorides An optional routine algaecide.
Cyanuric acid Alternate source of stabilizer.
/// QUIZ \\\
1. THE AMOUNT OF ACTIVE CHLORINE IN YOUR POOL DEPENDS ON:
A. THE WATER TEMPERATURE
B. THE ALKALINITY
C. THE pH
2. TO PREVENT CORROSION OF CEMENT POOLS ADD:
A. CALCIUM AND STABILIZER
B. STABILIZER AND BAKING SODA
C. CALCIUM AND BAKING SODA
3. THE BEST MATERIAL FOR CONTROLLING ALGAE IS:
A. QUATERNARY AMMONIUM CHLORIDE SOLUTION
B. COPPER CONTAINING ALGAECIDE SOLUTIONS
C. SODIUM HYPOCHLORITE SOLUTION
4. A CEMENT POOL SURFACE SHOULD LAST:
A. THREE YEARS
B. SEVEN YEARS
C. WELL OVER TEN YEARS
ANSWERS: In each case the correct answer is C. Not knowing these answers can
lead to increased costs, algae problems or expensive repairs.