For me I use gfo to control my phosphates. Once I see it rise up to 0.2ppm I would then replace my gfo. I find that in the past if I changed gfo when PO4 reaches 0.1ppm, I would go back down to 0 even if I used the smallest amount of gfo. Acros would brown out due to gfo stripping all the nutrients out.
I use Rowaphos to make sure I can maintain no higher than 0.10 ppm. I feed 6-7 times a day, so I have to use rowaphos and chaeto, and a sulfur denitrator for NO3.
No matter how much I feed (including Reefroids) mine stays at .03 or lower (Hanna checker). I stopped using filter socks a few months ago too. Nitrate is close to zero so I have less vibrant colors. I think I am going to start dosing to get Nitrate up a good bit and raise phosphate just a little.