Chelated Iron for Aquaponics

Iron deficiency in basil

Signs of Iron deficiency in Basil plants are yellowing of the leaves. Iron is an important nutrient for plant growth, but like potassium and calcium, fish food doesn't contain a enough to grow plants. Chelated iron a product that can be added to aquaponics systems so the plants maintain healthy and vigorous growth.

Which type of Chelated Iron?

Not all types of iron found around your house or at the nursery are suitable for aquaponics.

  • Chelated Iron found at hardware stores such as Bunnings is formulated for low pH soils, using a form of iron chelate called EDTA.
  • Rusty pieces of iron or nails around your home are iron oxide, which also isn't readily available for your plants if placed in your system

A healthy aquaponic system has a pH level between 6 and 7.5. EDTA Iron Chelate (Fe-EDTA) loses it's effectiveness on plants above a pH of 6, so doesn't provide enough iron for plants when used in aquaponics. DTPA Iron Chelate (FE-DTPA) is effective in a pH range of up to 7.5, which suits aquaponic systems.

edta dtpa addha iron chelate availability ph

Chart courtesy of https://www.akzonobel.com

Another form of iron available in hydroponic products is Fe-EDDHA. This form of iron chelate is a deep purple colour and is extremely expensive, so it doesn't look great in your water or make aquaponics cost effective.

How much Chelated Iron does an Aquaponics system need?

Plants show iron deficiency by growing yellow leaves with green veins. Iron has a number of important functions in the overall metabolism of the plant and is essential for the synthesis of chlorophyll. The most cost effective method of supplementing iron is with DTPA Iron Chelate which is a food grade nutrient available online or in store. Use 10g per 1000L to raise iron chelate by 0.5ppm, and most systems will require 20 to 40 grams of DTPA chelated iron per month.

Another source of iron Growth Technology Liquid Iron which supplements the three main types of chelated iron. It provides "available iron" to your system which is readily absorbed by iron-deficit plants. It is a food-grade nutrient designed for hydroponics, but can also be used for aquaponics at a reduced dose. Use 5ml of Liquid Iron per 100 litres to raise available iron by 0.5ppm, test and dose as required.

How to check for Iron in an Aquaponics system

Instead of diagnosing iron deficiencies via your plant's leaves, check the iron content within your system using an iron test kit. The first test checks for available iron - this iron can be readily absorbed by your plants and will disappear quickly if you have alot of plants. The second test is for iron chelate - the amount of iron in the water which is broken down into available iron over time. We recommend keeping the iron chelate level between 0.5 and 1.0ppm.

Iron Chelate from homemade fish food

Like potassium, iron can be supplemented organically and inorganically. Liver, soybeans, lentils, spinach, chard and kale are rich in iron and can be added to home-made fish food. To make your fish food, blend your vegetables using a high speed blender to get a consistent, fine puree. Freeze the puree and cut it out as required to feed the fish.