AFAIK with fish in the tank your iron doesn't want to be much above 1ppm -
any more than that doesn't do them a lot of good!
You will need to make sure there's enough NO3, PO4, K, GH(3 or
You can back off the traces, for a 20 gallon tank, the max amount
needed at high light etc is about 5 mls of Flourish/TMG etc every 3
More and you are wasting the stuff.
By doing 50% weekly watrer changes you can re set the tank each week
and ensure a relatively constant level of PO4/NO4/K etc by dosing the
following per 20 gallon tank:
1/4 teaspoon K2SO4 once a week after water change
" " " KNO3 2-3x a week
2-4 rice grain's worth of KH2PO4 2-3x a week
5 mls of TMG/Flourish 2-3x a week.
Do 50% water change which removes any dosing errors you made with the
other mid week dosings. Repeat.
Becomes old hat fast.