Introduction to Fertilizing the Planted Tank

In addition to CO2 and light, aquarium plants require nutrients in the substrate and the water for lush and healthy growth. The two basic categories of essential plant nutrients are macro and micro-nutrients. Macronutrients consist primarily of nitrogen, phosphorus, and potassium, while micronutrients include calcium, chloride, iron, magnesium, manganese, sulfur, zinc, and other trace elements.Plants are able to obtain some of these nutrients directly from the water, (i.e., nitrogen in the form of ammonia or nitrate from fish waste and other organic materials, and micronutrients and trace elements from the source water) but these levels are often insufficient for healthy plant growth. Plants in aquariums that use purified water are faced with greater challenges RO/DI water purification removes macro and micro nutrients.Without supplementation, plants are unable to thrive since natural concentration of nutrients such as potassium is relatively low. The nutrients need to be replenished routinely to maintain adequate levels, especially micronutrients, since many of them are utilized quickly and do not remain available for more than a few days.The two basic delivery methods of supplementing plant nutrients are substrate fertilization and liquid fertilization. Since some plants draw nutrients primarily through their roots while others draw nutrients through their leaves, each method has its unique benefits and application depending on the plant species. Proper supplementation leads to a balanced, beautiful planted aquarium that provides the added benefit of biological filtration and improved oxygen levels to your system.Substrate Fertilizers Substrate fertilizers are buried within the substrate bed. The nutrients are released slowly over time and are absorbed directly by the roots. They are ideal for root-feeders and have another advantage; algae cannot access the nutrients buried in the substrate. This minimizes unwanted algae outbreaks. Sometimes the substrate itself is rich in plant nutrients.Liquid Fertilizers Liquid fertilizers are an important source of nutrients for aquatic plants that absorb nutrients primarily through their leaves. In fact some plants don't grow roots into the substrate, so their only source for nutrients is from the water. The wide varieties of liquid fertilizers are easy to use and generally require regular use. However, a hobbyist must be careful when using liquid fertilizers since it is easy to over-dose, leading to conditions that favor algae.

MACRO NUTRIENTS (OR NPK)Nitrogen (N)

Nitrogen is generally supplied in the planted tank through ammonia, nitrite, and nitrate, which are compounds found in all tanks with fish. It is generally one of the first nutrients to require supplementation in the planted tank. It can be provided using liquid fertilizers commercially available, such as Seachem Nitrogen, or can be added using a dry powder form, via adding the compound Potassium Nitrate (KNO3).It is generally recommended that to provide enough Nitrogen for uptake by your plants, you want to keep your nitrate levels in your tank at 10-20ppm. Nitrogen deficiency in your plants will generally manifest itself as small yellowing or lighter colored leaves in new growth.Phosphorus (P)

Phosphorus is a macronutrient required for plant growth and health. It is generally used by plants in the form of Phosphate (PO4). Because of the harmful nature of PO4 to other aquatic life in your tank, we generally try to keep the levels very low. It is generally one of the last nutrients needed for supplementation because we can get by with very low levels, and PO4 is found in many of the foods we feed our fish, and the left over is more than enough to supplement our plants.It is generally added to the tank in the form of a liquid fertilizer such as Seachem Phosphorus or as a powder form as Monopotassium Phosphate or KH2PO4. We generally want to keep our tanks at 1.0-2.0ppm PO4, though I have had success in keeping lower levels of around 0.5ppm, especially in tanks with sensitive inverts.Phosphorus deficiencies manifest themselves as yellowing leaves in established growth, and can look very similar to nitrogen deficiency.I would not recommend dosing P in medium light or low light systems. It can easily cause algae problems, problems with fish and invert health, and is just generally not required in lower light setups. However, in high light setups, you will find yourself quickly bottoming out on P and causing nutrient deficiencies and algae problems if you do not dose it.Potassium (K)

Potassium is the 3rd and final macronutrient. It is a fairly benevolent nutrient when it comes to aquatic life, so there is not much harm in liberally dosing it. It along with N are often the first nutrients I would recommend dosing in low and medium light tanks. It is generally accepted that the desirable potassium (K) levels in a planted tank are 10-20ppm, but it can be dosed up much higher than that without issues. You can find titration tests for testing Potassium levels, but because it is not harmful in moderate amounts, it is easier to just dose more than enough to make sure you are covered. It can be dosed using a commercial liquid product such as Seachem Potassium, or can be added as a dry powder in the form of Potassium Sulfate, or K2SO4.Potassium deficiencies manifestas yellowing leaf edges or small pin holes in leaves, especially in established growth.

MICRO NUTRIENTS OR TRACE ELEMENTSThere are also several other organic and inorganic compounds and elements that are required by plants to remain healthy and grow, but are needed in far less concentration. We generally refer to these as trace elements. There are several elements and compounds on this list, including magnesium, chelated copper, chelated iron, manganese, molybdenum, zinc, cobalt, and a few others.They can be dosed using a liquid trace mix such as Seachem Trace, or can be dosed as a dry powder using a product such as Plantex CSM+Boron. Often people will chose to dose Chelated Iron separately from other trace elements, though most commercial trace mixes do include some level of Chelated Iron.WHAT TO BUY?It really depends. There are so many forms of supplementation for the planted tank. You can buy nutrient rich planted tank substrate such as aquasoil or ecocomplete. You can buy root tabs for heavy root feeder plants root tabs usually provide trace elements and 1 or more macronutrients. You can buy liquid mixes such as Seachem Flourish, which is a source of Potassium and Trace elements, with a small amount of Nitrogen supplementation, or API Leafzone & Tetra Florapride, which are primarily trace and potassium mixes. You can buy individual liquid supplements such as the seachem line as I outlined above, or you can buy dry powders of each.What I would recommend depends greatly on the types of plants you are growing, the lighting, the CO2 levels, and the deficiencies that your plants may or may not be exhibiting.As a general guideline though, my recommendations usually go something like this:1. A liquid mix like Seachem Flourish, or API leafzone for low light tanks and beginners who are looking for some supplementation. These products generally wont cause too many issues if dosed as the directions state.2. Individual liquid doses for macros and micros for medium light tanks and those still newer to planted tank supplementation and planted tanks in general. The seachem line of individual solutions of N, P, K, Trace, and Iron are a great place to start. Pfertz also makes some very good individual dosing solutions.3. Individual dry powder doses of N, P, K, and Trace for high light tanks and for those more experienced. This is the best way to dose as far as economics, as dry powder is far cheaper in the long run than liquid ferts with liquid ferts you are paying mostly for water. It also offers a lot more flexibility in controlling individual nutrient levels to hit specific targets, as opposed to using mixed solutions of liquid ferts.

DOSING METHODSWhile I intend this to be just an intro, and deep discussions of individual dosing methods are beyond the scope of this article, I will mention a few of the more common methods. Google can be your friend here to help you determine which dosing method is right for you.Estimative Index (EI) DosingEI dosing became very popular a few years back and is a very easy method. Essentially it involves dosing each individual macro and a trace mix up to a high level during a weekly water change. At the end of the week, a 50% water change is performed, cutting the remaining nutrients in half, and the tank is dosed again. This is a simple way to insure you never bottom out on any nutrients.Target DosingTarget dosing involves performing water tests on Nitrate, Potassium, Phosphate, and Iron levels and dosing according to the target levels for your tank.PPS Pro DosingPPS Pro dosing has become very popular in the last few years. It involves dosing the tank with the amount of each nutrient needed during a 24 hour cycle. It requires daily dosing, but is great for keeping the tank from having excess nutrients which can cause algae issues. It does involve some math and some pretty small measurements, but is a very effective way to dose. There are some great build threads out there on making autodosers for pretty cheap that work well for this method. That way the daily dose is delivered automatically.