Aquarium Plant Fertilization

Fertilization of aquarium plants has been a problem from the start because of the varied and specialized habitats that the plants come from. Aquatic plants have special adaptations for the uptake of water and nutrients. The watery environment also offers nutrients differently to normal plants.

Nutrient Absorption

To know what nutrients to give aquatic plants it will help to understand how they absorb nutrients. Generally aquatic plants can absorb nutrients through their leaves and their root systems unlike normal terrestrial plants that absorb most of their nutrients from their roots.

Generally aquatic plants have a very thin or no cuticle on their leaves and stems as they are in no danger of drying out. This helps with absorption of nutrients as well but also makes the plants more vulnerable to damage and disease.

What Nutrients

All plants require an uninterrupted supply of 14 nutrient elements to grow properly.

These are the Macro-nutrients:

And the micro-nutrients:

All these nutrients are needed by plants but the proportion they are given to the plants in is where aquarium plants and normal plants differ. I am not going to talk about each indivdual element but rather the macro and micro-nutrients as a group.

Algae is the Enemy

Normal fertilizer mixes made for garden and pot plants are made with large quantities of the macro nutrients and small portions of the micro-nutrients.

These are unsuitable for the aquarium. The main reason being that these cause algae blooms.

Algae is one of the main problems in aquariums and is normally from incorrect fertilization. Algae needs large quantities of macro nutrients and if it gets these they will generally grow wild and cover the glass and plants ruining your chances of getting a good looking aquarium and also choking your plants.

Plant Fertilizer mixes

A good aquarium plant fertilizer mix differs from a normal fertilizer by having very few or no macro-nutrients. The main reason for this is algae as mentioned above.

The macro-nutrients in the aquarium should come from water changes (tap water normally has all these nutrients in small amounts) and small amounts from the fish. Water changes should be done at least every 2 weeks and about 15% should be drained and replaced. This should supply sufficient macros.

The micro-nutrients are different and are normally in short supply in tap water. The other problem with the micro-nutrients is that they are very unstable in their inorganic form and normally precipitate and become unusable.

The Chelate Breakthrough

The discovery of an organic molecule the chelate which binds to metal-ions tightly allowing them to be dissolved in a water solution with no precipitation so making the nutrient available to the plant. This very important for aquatic plants which normally have a very large appetite for iron and may need as much as 4ppm to allow healthy growth without chlorosis.

Chelate Types

There are six types of chelates important to hydroponic growth but only two that need to be mentioned for aquarium plants both for production and in the aquarium.

EDTA (Ethylene-Diamene-Tetra-Acetic-acid) is the first and most commonly known. This is not ideally suited for aquatic plants because it is unstable at a higher pH than 6.0 and generally aquarium conditions are between pH6.0 and pH8.0. This is also a cheaper chelate and so is unfortunately used to cut costs, so absorption is limited.

DTPA (Dethylene-Triamine-Penta-Acetic-acid) would be a better choice and should be more widely used because it is stable up to a pH of 7.5. This is within the aquariums conditions.

A Good Aquarium Plant Fertilizer

When looking for a fertilizer as a very general rule look for:

  1. Preferably a liquid
  2. Low or No macro-nutrients
  3. High Iron (Fe) in the chelated form
  4. All the other micro-nutrients also in a chelated form if possible

There is still a lot of experimentation needed in the aquarium but the plants are getting to be of a higher quality all the time and people are putting more time into the development of fertilizers.

It must also be noted that fertilizers for the production of aquarium plants are not suitable for the aquarium and will cause problems (mainly algae).

Echinodorus martii
Echinodorus hybrid plantlet
Newly planted Ambulia

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