Most of the nutrients required for growing terrestrial plants in an aquaponics system are provided by the wastes from the fish. There are a few trace elements that may not be provided without some form of either adjustment or supplementation.
Iron deficiency in your aquaponic garden is one of these possible lacks. In a recent article written for the the Aquapononics Source titles Iron deficiency in Aquaponics the problem is defined:
Depending on the type of plants you are growing, the quality of the feed you are feeding your fish, and the quality of your water, you may never have an iron issue. So how do you know? There are really two ways. The first is a visual test. If the leaves on some of your plants are starting to yellow, but the veins in those leaves remain green, your plants probably have “chlorosis”, a condition caused by insufficient iron. But what if you want to spot the problem before your plants show these signs? You can by using an Iron Checker by Hanna Instruments. With this handy little device, you will quickly and easily be able to read the amount of iron in your water in ppm (parts per million). When you take your reading, remember that your target range should be 2 – 3 ppm. When you get to about 1.5 ppm, you will start seeing those yellowing leaves indicating an iron deficiency.
When you discover that the iron content in your water is too low and you so, indeed, have an iron deficiency for the plants, either by an iron test kit or through the diagnostic inspection of your plants, you should add an iron supplement to the water. There are plenty of Aquarium plant fertilizers that will do this, but they should only be used when the iron content has dropped. Unlike most fertilizers that can offer a regular dosing schedule, iron needs to be carefully monitored before it is added. As such, most quality iron additives do not offer a standard dosage for any time period.
Iron Deficiency and pH
Another problem is the ability for iron to remain properly chelated depending on pH. The most common chelated iron supplements for iron deficiency are active only up to a pH of 6,5. This may be fine for an acid South American tank, but when the ideal pH is 6.8 – 7.0. the chelated iron should be in the form of Fe-DTPA. It is a little more expensive,but more stable at higher ph. If you re going to take the time and trouble to test the system for iron deficiency, you might as ensure that the product used top solve it is effective at the pH you should be targeting.