Quote Originally Posted by jimsflies View Post
So you think it is the rock because you eliminated the other possibilities? Do you also have substrate in the tank?

Perhaps if you take a piece of rock out and put it in another tank that you know has zero phosphates, and then test that water after a week of just having a piece of that live rock you could verify it is the rock.

Are you also sure that you are using enough of the GFO and replacing it frequently enough?

Also what test kit are you using for your phosphates? I assume you are having a big algae issue?
I agree with Jim, there is a good likelihood that it is your substrate and not the rock. However, DON'T stir up the substrate until you decide to change it out. Stirring up the substrate will release toxins and chemicals that have saturated it and will cause a fish kill or worse.