[Jim_PA]

Iron Chelate 13% or 10%

I am thinking 13% since it less money.

 

[In.a.Box]

Clay ^^
Depends on the iron lvl already in the tank.
The max ppm is 1 or 2

 

[HD Blazingwolf]

either works fine.. go with the 13 but keep in mind it can stain ur water brown pretty easily

 

[Jeffww]

I really like ferrous gluconate. It dissolves really easily. But ideally you'd use a mix of both since various chelating agents will work better at varying water conditions.