A warning about gfo: I put 1/4 of the recommended dose in a reactor, and Ho estly, within a week, my sps started to lighten up and I didn't have to Clean my glass for 2 weeks. I had to take it off, because my chaeto stopped growing, and started to look like it was starving. I'll use gfo with my new rocks if the P04 is high. Otherwise, I'll just plop some chaeto or macro in the fuge again