Re: Iron solubility
At pH values commonly seen in aquaria (6.5 to 8) the amount of FREE Fe+3 in
solution is very low. Iron in oxygenated waters forms iron oxides and
hydroxides that basically precipitate as rust. They coprecipitate
phosphate and other metals. If you dont believe me, check a speciation
chart for Fe in solution. Chelation is the only way to deliver adequate
amounts of iron to plants via the water column. BTW EDTA complexes iron
as the Ferric (+3) ion.
Biologically, the valence state of Fe makes all the difference in the
world ... its precisely because of its redox properties that makes Fe one
of the central atoms in photosynthesis and respiration.