How much GFO?

[Reef Pilot]

I don't go by any calculator, just what fits nicely into my refillable canister cartridge which is about 250 ml.This is for a 230g system. I use HC GFO. It last about 2 months for me.

I try to keep my P04 between 0 and 0.04 (Hanna). After a change my P04 goes to zero. I check every 2 weeks or so. When it climbs to 0.04, I stir it up in the canister and it then returns to zero. I usually do this 2 times with the same batch. If it doesn't return to zero, then I know it is time to change.

This routine has been very consistent for me. And keeps my GFO costs down. And my P04 doesn't get out of hand. I find best SPS color and growth at these low levels of P04.

Last year I had some tank troubles and my P04 jumped up to as high as 0.10, and had to increase my GFO changes to get it back down again. My SPS lost color, and growth really slowed. I should mention that some SPS are affected more than others. Some didn't seem to be affected at all. But no question, overall and in general, all SPS does better with low P04.