Fertilization methods for planted tanks

There are many ways to provide food for aquarium plants. Depending on the general setup of the planted aquarium (light intensity, photoperiod, CO2 supplementation, water pH and hardness) dosing/fertilizing/feeding the plants can be done once a week, twice a week, 3 times a week or sometimes daily. Many methods have been developed to ensure that plants get the right amount of nutrients. But before this article discusses the types of dosing let us first touch on what to dose which is more important.

What are fertilizers?

         Plant food can be categorized into 2 major sections.  The Macro and Micro fertilizers. The categorization of these plant fertilizers is based on the amount of each nutrient needed by plants to thrive. Plants need more macro fertilizers than micro fertilizers.

Macro fertilizers

Macro fertilizers can be divided into 2 categories. The important macronutrients are Nitrogen, Phosphorus and Potassium, and the minors would be Calcium, Magnesium, and Sulphur. People who have a background in gardening are familiar with these since they are always found on labels of plant fertilizers in the form of N-P-K. The minor fertilizers need not be discussed since plants get these mostly from the water and in the soil. The planted tank itself already produces Nitrogen in the form of nitrates which is a by-product of the nitrogen cycle in filters so one would not need to do a lot of these. Phosphorus would also be present in large amounts in fish waste and in fish food. What the planted tank lacks is an adequate supply of Potassium. This is what needs to be dosed more than the other major macro nutrients.

Micro fertilizers

         Aquarium plants would still need micronutrients but in a far less amount than macronutrients. Out of all the micronutrients, iron is the most important to regularly dose in the aquascape. Certain nutrients like Molybdenum, Borin, Copper, Zinc and Manganese are still required but in far lesser amounts.

        Like terrestrial plants, aquatic plants do need these nutrients for them to photosynthesize and thrive. Unlike terrestrial plants though, aquatic plants can not have these nutrients in excess since they are in an enclosed environment where excess is food for algae to take advantage of. The function of tank dosing or fertilization is to provide just the right amount of food for the plants, just enough for the plants to consume within a few days or within a day.

         When discussing the subject of fertilization of the planted aquarium there are 2 things to consider. One is that nutrients can be found in the water column and that plants do rely on those nutrients as an immediate source of food. Second is that nutrients can be found in the substrate itself which established plants would come to rely on should nutrients in the water column become scarce.

Introduction to methods of fertilization

         There are 2 opposing theories of water fertilization. The first is that the tanks need to have a nutrient-rich substrate and fewer nutrients in the water. Nutrients in the substrate itself when locked and not leaching out into the water column is a long-term source of food for the plants. This is where vulcanic soil and clay become very good substrates for aquatic plants. They have a high Cation Exchange Capacity which translates to the substrate absorbing the nutrients and locking it in.

         The second theory is that the substrate can be inert. It does need to contain a lot of nutrients for as long as there are nutrients present in the water column always. That would mean the tank needs to be dosed at a far more frequent and consistent rate than with the first theory.

A lot of tanks have been successful using either theory number 1 or theory number 2. A combination of both theories while possible and very effective is also very dangerous as it may result in an excess of most nutrients which can lead to unhealthy plants. Unhealthy plants can trigger unwanted algae blooms.

The ADA Style of Dosing

         Designed by the late great Takashi Amano, this type of dosing would rely heavily on the nutrients locked in the substrate and would be considered lean dosing. This follows a lesser frequency of dosing the water column. This can be considered lean dosing. It only provides very lean amounts of Nitrogen, Phosphorus and Potassium as well as the micronutrients in the water. This type of fertilization would ensure that no excess nutrients would be available for algae to thrive on.

         There are certain additives that are placed or mixed with the substrate before planting starts. This is to ensure the plants would have a sufficient amount of nutrients to tap into for a certain period of time. Water column dosing would then just be secondary. There would come a time when the nutrients in the substrate would be depleted but fertilizing it through nutrient capsules should replenish it and therefore extend the life of the aquascape.

         This method works especially well if plants that have the same nutrient and light requirements are grouped. It may have challenges if heavy column-feeding plants are mixed with plants that have no special requirements. 

Estimative Index

         The Estimative Index ensures that all nutrients are available for the plants to use all the time. Formulated by Tom Barr, Estimative Index dosing requires frequent dosing of the water column and not relying so much on the substrate as a source of nutrients although nutrients in the substrate would not affect this method.  Excess amounts of nutrients in the water column would then be reset by carrying large amounts of water changes sometimes going up to 50% to 70 % a week. This method removes nutrients as a limiting factor for growth. While the nutrients in the water column of the E.I dosing can be up to 20 times more than the ones found in the ADA method, the plant growth is way much faster as well compared. The aim for this method is maximum plant growth.

         If not done properly though, this could result in too much amount of Nitrogen in the water which could affect the red coloring of certain plants. Leaner Nitrogen levels are necessary to bring out the bright coloring of some plants like some species of Rotallas and Ludwigias although the nutrient level is not considered as the main factor that could bring out the reds in some plants but rather the lighting.

         This method exerts that the presence of excess nutrients in the water column in itself is not a trigger for algae growth for as long as the plants are all healthy and thriving.  Mostly algae are triggered by rotting organic materials in the tank. Still, there is a limit as to how much excess the aquatic plants can tolerate that is why there is a guide on how much of the nutrients should be dosed and when to dose it in the tank. Too much and the plant basically shuts down all functions refusing to photosynthesize and absorb these nutrients.

Observation is the key!

        There are hybrid methods combining both the rich substrate of the ADA method and the rich water columns but as mentioned previously there is a danger in this when not done properly. These 2 opposing methods should serve as a guide to every hobbyist, both newbie and experienced. The dosage and ratios of these 2 methods have been formulated so that the hobbyist will no longer perform frequent testing of the water to determine how much CO2, Nitrogen and any other nutrients are present in the water. Just remember that no 2 tanks are the same. Following either of these 2 would still require some observation and tweaking. Adjust doses according to how the plants in the tank react. They should show the hobbyist what is lacking if the hobbyist only knows what to look for and what to observe. Check the color of the leaves, look for any abnormal growth patterns and know the symptoms of nutrient deficiencies. The plants themselves will show as well if they are happy. There is a very big visual difference in the plant that receives all the nutrients and requirements than the plant that is lacking or having too much of those nutrients.   


Both popular dosing methods have their own way of dealing with excess nutrients in the water column. Excessive nutrients may not be a trigger for algae but it will certainly alleviate an algae problem if one is to ever occur. It is mostly in how the tank is maintained though that is in question if there is algae growth. It could be not enough filtration, not enough water flow or not enough water changes or too much light and too long of a photoperiod.

Try to find a dosing method that works for the tank and stick with it. It may require some minor adjustments from time to time given that the plants are growing and would require more and more as each day goes by. The most important part of anything applied to the tank is that one observes the tank on a daily basis. This is after all why one gets into this hobby-to observe and enjoy.

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