If you started out with all that at once that is likely the reason for some minor instabilities. A wise man once told me; "In a reef tank no rapid change is good, even a change for the better." start with small amounts of GFO and progress to more, it may shock the system to start with a lot. If you are referring to the phosban 150 being half full that's actually quite a bit. I wasn't even a quarter full on my 180g system after long term use.