coming from http://2the4.net/iron.htmThe time required for uncomplexed ferrous iron to undergo oxidation to the ferric state is dependent on many factors, the dominant being: pH; temperature; dissolved oxygen level; and the presence of other soluble ions. The lower the pH and temperature the longer the time required for completion of the oxidation reaction. Increasing dissolved oxygen decreases the time required for oxidation. For example:
At pH 7.0, 90% Fe+2 oxidation requires 1 hour at 21o C and
10 hours at 5o C. At 21o C
At pH 8.0, 90% Fe+2 oxidation occurs in 30 seconds,
at pH 6.0 it requires 100 hours.
The critical dissolved oxygen concentration is 2 mg/L. Below that ferrous iron oxidation occurs slowly.
It's a sliding scale... In my case (and I am just one of many many cases), I concluded that UV light (from my Coralife TT UVS) was causing the precipitation - in MY tank. UVS off, Fe tested 0 - clear water. UVS on, Fe tested 0 - clear water. UVS off, Fe added (3 different varieties - 3 separate exercises - dosed.5ppm Fe - test confirmed concentration) - clear water. UVS on, Fe added - hazy water for 48 hours. When water cleared after two days, Fe was tested - 0ppm. *If Fe was dosed, and the UVS was left off, Fe stayed in measureable amounts for weeks.I'm assuming you've read up on iron. So what's causing this?