If I recall correctly, photoreduction should not occur with Seachem's iron as the Fe is already in its reduced state as ferrous gluconate. The loss of useable Fe is more likely due to the relatively fast spontaneous destablization of the weak gluconate chelator.dennis said:
Fe and PO4 react to form insoluble iron phosphate compounds so keep the macros and micros in separate containers. I don't think that anyone will be able to quantify, without much difficulty, the degree of this precipitating reaction.
:rock: [smilie=d: :rock: