I have a 91g system with an 18g sump - it's a Red Sea v3 sump with a dedicated fuge chamber. I have bio balls on the base and a Tunze fuge light for growth. I run the light 12 hours, at night when the DT lights are off. The tank sits at about 10-15 no3 and 1.1-1.2 po4 (I know, it's high!). I've tried Chaeto three times now, each time it's died off. I added another hefty chunk of it last week and I can already see it starting to lose its color and die off. What gives?