In aquaponics, it is not uncommon to encounter deficiencies or, more precisely, a lack of minerals in our aquaponic system. There are several, but some have more consequences than others on flowering and chlorosis (leaves turning yellow). In this article, we will try to understand where it comes from and what we can do to remedy it.

First, it is important to understand how the system works, otherwise, it will not make sense and you will not be able to take countermeasures if you ever have deficiencies. In an aquaponic system, we use fish to grow plants.

How does the system work?

The only input in the system is fish food. The fish will therefore produce waste that is organic matter not assimilable by the plants. Thus, we will have nitrification or the nitrogen cycle. This will produce almost harmless ammonium and ammonia which is very toxic. It will all depend on the pH, notably.

Next, there will be bacteria in your aquaponic system that will transform this ammonia/ammonium into nitrites which are just as toxic to fish. Other bacteria will also transform the nitrites into nitrates. But these nitrates, on the other hand, are not very dangerous for fish and will especially have the good property of bringing nitrogen to your plants since it is in this form that plants can recover nitrogen which is essential for their growth.

With these same wastes, there will be other bacteria that will extract the minerals contained in them (phosphorus, calcium, potassium, iron). And so, we move from an organic world to a mineral world. These are therefore minerals that have been dissolved in the water. And when they are dissolved in the water, they will be able to be absorbed by the plants.

In theory, if the food contained all these elements in sufficient concentration, the system would be self-sufficient. Everything would be provided by the food absorbed by the fish which produce waste. The bacteria will transform all this and everything will be provided to the plants. It would be pretty much the perfect system.

Except that in an aquaponic system, we try to recreate what nature produced and therefore, it is a bit more complicated than that.

The role of pH in mineral absorption.

It is depending on the pH that we will know if the plants will be able to absorb the minerals or not.

You can therefore put as much iron as you want in your system. On the other hand, if your pH is too high, the plants can lack iron (aim for a pH between 6.8 and 7). This is the threshold that is the most favorable and which will bring the maximum of nutrients to your plants.

Let's take an example: we can see that the need for minerals differs depending on the plants. Lettuce, for example, does not need much. In a deficient system, you will not necessarily see it. On the other hand, for basil or strawberries, if you have an iron deficiency, it will be immediately visible, that is to say you will have leaves that turn from green to yellow. So the three most frequent deficiencies in aquaponics are calcium, potassium, and iron. From time to time, you will have a magnesium problem, but that is because, in fact, it reacted with the calcium and potassium. Everything is not independent.

How to detect deficiencies in aquaponics and how to remedy them?

There are two methods to know if there are deficiencies in aquaponics:

• Visual observation
• Perform chemical tests

By visual observation, you will be able to say that there are deficiencies if you notice leaves that turn yellow, turn black or fruits that have problems. Then, you can try to understand where these deficiencies may come from by looking on the internet.

To perform chemical tests, on the other hand, you can find pH testers or magnesium/calcium testers on the market. All that will be left is to test the water of your system afterwards.

Once you have concluded that your system has deficiencies, you will have to remedy it. Two options are available to you:

• enrich your fish food or,
• add supplements.

If you want to add supplements, opt for DTPA chelated iron. EDTA iron is less suitable: it remains less available to the plants when the pH rises. For calcium, you will be able to buy calcium hydroxide powders that will dissolve in the water and be absorbed by your plants. Same for potassium, opt for potassium hydroxide. By adding calcium hydroxide and potassium hydroxide, you will be able to raise your pH. In general, in a well-balanced aquaponic system, nitrification will naturally lower your pH and will lower it so much that we will be outside the optimal zone and therefore, the maximum absorption of nutrients. So, adding these supplements will allow you to increase your pH and get back into the right zone, that is to say 6.8 / 7.