Mysterious Iron in Aquaponics
Given an accurate instrument (Hanna Fe Checker) and lab results (OSU CAL) to measure iron, and assuming containers of name branded OMRI chelated Biomin Iron 5%, actually contain such concentration, over the last 14 days I have added over 48 ounces of concentrate to a closed organic aquaponics system of about 3300 gallons and am reading approximately zero ppm with a pH of 6.5. Can there be a chemical explanation for the apparent lack of iron?
Lincoln County Oregon aquaponics
I haven't worked with one of these aquaponic systems but the amount of biomin iron that you have added would indicate that the actual pH of the water might be higher than your meter is reading. The other thing I found online is that they were adding about 16 oz. of 13% iron once a month. You added 48 oz. of 5%. proportionally you added about 14% more Fe without getting results. You may have already seen this article I found online that does discuss some of your issue. They seemed to be saying all the systems work a little differently so you may just need more iron.
They mentioned Fe deficiency and N deficiency in the article both having similar symptoms except the N deficiency is just on the older leaves while the Fe is on old and new leaf growth. I figure you already know this but just incase I thought I would mention it. Here is a link to the article I found.
Sorry I don't have more experience with these systems.