Probably because coral 1) requires better quality water and

Could you be more specific? What do you mean by "better quality water"?
My nitrites, nitrates and
ammonia levels are undetectable using store bought tests. My phosphates are
also very low. My salinity is also on target. I dose with Kent Marine
Essential Elements every three weeks.

2) is part of the definition of a "reef" aquarium.
George Patterson
Coffee is only a way of stealing time that should by rights belong to
your slightly older self.