Personally I run GFO all the time, test regularly, and whenever I see detectable phosphate on at least two consecutive tests, change out the GFO. No particular time schedule. I've also noticed that I don't really need to test to know when my PO4 levels are up. My corals just generally don't so as well, I get noticable browning, and it's the ONLY time I ever get any algae issues from hair algae to slime algae to cynao (very mild and never get any of that otherwise).
|