well azoox feeding is pretty diverse as many corals do not make energy via photosynthisis.
things like sun corals and dendrophyllia will take large meaty foods into a large polyp (LPS)
others such as gorgonians will take zooplankton and phytoplankton into smaller polyps.
chillis, denronepthyea, some sea fans etx will only take very small planktonic life and need near on constant feeding (not the chilli)
the food pollutes the water as alot of it isnt eaten, in the ocean this doesnt matter as it will decay and feed algae/ planton/ bacteria etc. in the closed system this has no where to go, rots and produces ammonia and phosphates which as you know are bad
i could go into much more detail but the above sums it up without me writing to many long words.