too much Gfo

[sea dragon]

when using the recommended amounts po4 stays up but when I am using three times the amount the tank stays at acceptable po4 levels otherwise it just won't. Even with water changes.

 

[Randy Holmes-Farley Verified Community Expert]

The "recommended amount" provided by any given manufacturer is just an estimate for each tank. Every tank has different export needs so will be best served by different amounts of GFO, from none to a lot more than "recommended".

How often you replace it also plays a big role.

I discuss GFO in detail here:

Iron Oxide Hydroxide (GFO) Phosphate Binders by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2004-11/rhf/index.htm