Eienna, to save Glenn from repeating himself, I asked him that on the last page of this thread, and he said its iron citrate hes using. Randy has explained how to make this elsewhere, although he currently recommends a different iron supplement himself (iron gluconate), and in case you can't find it online as I could not, hes just helped me understand how he made it in the past in this thread
https://www.reef2reef.com/forums/re...-mono-sodium-citrate-making-iron-citrate.html
In a nutshell, he adds 25g of ferrous sulfate heptahydrate to 50g of trisodium citrate dihydrate, both easily available on ebay, to 250ml of water, and doses that, at a rate of about 0.1 to 0.3 ml / liter tank volume, 2 to 3 times a week (thats Randy's use for algae nutrients). Glenn's dosage is about 0.15 ppm (once weekly IIRC), although I am not sure if thats 0.15 ppm iron, or 0.15 ppm iron citrate - maybe Glenn can clarify? My chemistry is not quite good enough to be able to convert that dosage in ppm to ml of the above solution, maybe someone else can calculate it?
To have a bit of a guess, to dose this mix at 0.15 ppm I *THINK* (and stand to be corrected) you would need roughly 7.5 microliters per liter tank volume, or 0.75ml per 100 liter tank volume, if the final volume of Randys iron citrate was 250ml (which it would not be, it would be more, but this is probably good enough and would result in under dosing rather than over dosing). To be more accurate you would need to multiply this (7.5 microliter / liter tank volume) by (final volume of citrate mix / 250).
Sorry I am using metric but its too hard for me to use gallons and ounces etc.
Be aware that this will contain a carbon source in the form of the citrate.