Tom: <<<<As mentioned above the anaerobic bacteria will break down waste and use up oxygen. >>>>> Anaerobic bacteria do not use oxygen for their metabolism, facultative anaerobic bacteria may or may not use it, aerobic bacteria need oxygen for their metabolism. The latter is the group we are talking about. Phospates are not particularly toxic compounds, and are in fact added by water companies to soft tapwater to protect pipes from corrosion. Not a likely cause of health problems. Thanks for the additional info. By the way, if anybody is living in the Teanek, NJ area, yesterday at Reef Encounters I saw several, decent-looking A. cacatuoides on sale at 2.99 $ each. (no private interest in that store). Dionigi