Iron is more readily absorbed in pH of 5 -6.5. Our tanks are probably not going to be at that level so I wonder how well any iron fert is absorbed by plants with this in mind. So, the lower your pH, the greater the iron absorption? My thoughts are, higher pH tanks may have issues because of this requirement unless the iron is specifically made to work in the higher pH aquaculture. I wonder if Flourish takes this acidity into account, and if there is a difference in the type of iron in Flourish, and the type available from cooking? I have never really thought about it.
Another interesting tidbit I copied:
'Acidic foods that have a higher moisture content, such as applesauce and spaghetti sauce, absorb the most iron. For example, one study published in the Journal of the American Dietetic Association found that the iron content in 100 grams of spaghetti sauce jumped from 0.6 mg to 5.7 mg after being cooked in a cast iron pot. Other factors that boost the iron content of foods include longer cooking time, frequent stirring, and using a newer iron skillet.'