Chelated Iron for Aquaponics

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After a while, plants may develop yellow-colored leaves with green veins, indicating that they may be iron deficient. Iron deficiency in plants is a widespread issue. But, this issue can be easily remedied.

Typically, signs of iron deficiency should not escalate beyond the discoloration of the leaves. Yet, chlorotic foliage, deformed or distended new growth, also indicates an iron deficiency in plants.

If you have been observing these signs in your plants, you should definitely feed them iron. 

Role of Iron in Plant Growth and Metabolism 

Iron is an essential nutrient for every kind of plant and one that you need to include in the soil testing program on your farm. Iron has a lot of different roles for plants.

Being a group nutrient containing several enzymes, iron plays a vital role in many physiological and biochemical pathways in plants.

One of the several things it helps with is chlorophyll production. In addition to that, it helps with :

  • Respiration
  • Photosynthesis
  • Nitrogen fixation in legumes

Iron is considered a micronutrient, but don’t let the name fool you because iron is needed in the highest amount as far as the micronutrients are concerned.

Iron is typically one element that most growers have experienced problems with, either due to deficiencies or toxicities.

More about Iron Deficiency 

Several things typically cause iron deficiency: 


As the pH of the growing plant increases, iron deficiency tends to become more of a problem. As pH goes up, iron becomes less available for plant uptake.

Typically you want to try to keep the pH of your plant between 5.5 and 6.2. If you start going above 6.5, it becomes difficult for the plant to obtain the iron. 

Application Rate

The second thing you want to look at is your application rate. As with most complete fertilizers, if the fertilizer’s application rate is low, that means we’re providing fewer micronutrients, including iron.

It might be a useful idea to look at increasing your fertilizer application rate. In some cases, most fertilizers do not provide enough iron for crops, such as the Calibrachoa and Petunia.

In that case, it might be good to supplement with what we call an iron chelate which will provide additional iron to the plant. 

What is Chelated Iron?

Chelate word is derived from the Latin word chele, which means “lobster claw.” Chelator molecules are used to form a tightly closed claw around the metal ions to make it easier for the plants to take in the nutrients.

They are small molecules that bind to metal ions to increase the availability of micronutrients like iron. Some plants with overly irrigated soil types can lock up the iron nutrients, making them unable to reach the plants. 

Since plants are unfit to consume iron independently, the iron becomes worthless to them, causing iron deficiency. In such cases, a chelator is used to shield iron from decay and prevent it from leaking out of the soil.

This way, it can preserve it in a state that plants can use.

Chelated Iron for Aquaponics

Aquaponic Systems are typically deficient in iron. So, adding iron to aquaponics is necessary for optimal plant health.

To make iron that is available to plants, the iron must be chelated. Iron chelate is water-soluble and is easily absorbed by the plants. 

Understanding the Aquaponic System and Chelation 

F++ Ferrous Iron F+++ Ferris Iron 
Soluble Insoluble 
Low pHHigh pH

Most aquaponic systems are aerobic and have relatively high pH, which is bad for the plant. It means that most of the iron which is present in the system is unavailable for the plant.

This issue is not uncommon in the plant world as, over time, plants have developed many exciting ways to get iron out of the system. 

One thing that plants do is secrete hydrogen ions across their roots which acidify the water right around their roots, making iron more available to the plant. 

Also, one of the fascinating compounds developed is chelating agents. In plants, they are called Feitosa Dara Fors. But there are a whole bunch of different chelating agents out there.

When we talk about chelation, we are basically just talking about making ferric iron that converts insoluble iron into soluble one by attaching a unique molecule. 

These molecules are usually things like amino acids and other organic molecules. These molecules bind to ferric iron, which is insoluble and has high pH.

It makes it so that it can dissolve into the solution and move through the system. Eventually, it will find the plant root, and the plants will be able to absorb the iron. 

Some of the chelated irons used on fertilizer labels are:


The Fe-EDTA chelated fertilizer is one of the worst chelated fertilizers to put in your system for many different reasons:

  1. It is a toxic form of chelated iron.
  2. It is mainly used as a herbicide to kill certain plants.
  3. It only works and is stable up to a pH of about 6.3.

These reasons mostly defeat the purpose of delivering iron, and one should not use toxic substances in their system. It is often sold as a type of iron to be put into aerobic systems. People that use this in their aerobic systems are wasting their time and money.

Often they don’t understand the effect it could have on their system. Thus, it is highly recommended to stay away from this chelated iron fertilizer. 


This iron chelate is nontoxic and commonly used in systems as it works really nicely and is pretty effective. It comes in a reddish-brown powder which is typically dosed in our systems.

It is available locally and is pretty inexpensive. This one is effective up to pH 7.5, which works well in making the iron available to the plant even in aerobic conditions. 


This one is a little bit harder to find, but it’s highly recommended and works very well. It works up to a pH of about 9, which is incredible.

Almost all beginning systems that are showing some iron deficiency should be using this chelated iron. 

How and When to Apply Iron Chelates

The industry standard for chelated iron is 2 milligrams per liter every three weeks, equivalent to 7.58 milligrams per gallon.

Dr. Rakocy developed this standard dosage at the University of the Virgin Islands. This dosage has been what everyone has used ever since. 

Chelated iron is not pure iron but is a percentage of pure iron, and it is recommended to calculate based on the amount of iron present in the powder.

If you look at the label of your chelated iron, it will show 6 or 11-12 percent iron. The Fe-EDDHA is the one with the lowest concentration of iron at about 6 or 7 percent. 

Trying to apply iron to plants without a chelator might be a waste of time and resources since the plants will not be able to absorb sufficient iron until it combines with oxygen or is siphoned from the soil. 

Fertilizers specializing in chelated iron are readily available in many different forms like spikes, pellets, granules, or powder.

The fertilizers, which come in grains or powder, can also be used as water-soluble fertilizers or foliar sprays. Spikes, slow-release granules, and water-soluble fertilizers must be put on following the plant’s drip line to get efficient results.

Foliar chelated iron sprays should not be sprayed on plants on hot, sunny days.

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