I was using GFO on a daily basis for about 9 months to keep po4 down (about 20% less than BRS's calculator recommends for my 43 gallons total volume) but recently stopped after getting a chaeto reactor up and running and seeing that it has been just as effective in controlling po4 and even keeps that tiny trace amount I want in the water. Shout out to Somatic for giving away those reactors at RAP California! =)