Sometimes aquariums can be too clean, believe it or not. Corals depend on a certain level of nitrates and phosphates to feed zooxanthellae, and stripping your aquarium of these nutrients can cause corals to bleach out. This problem is prevalent in bare bottom aquariums and reef tanks using various forms of chemical and bacteria-based filtration. For these aquariums, it’s wise to house multiple large fish and feed heavily. Keep phosphate and nitrate levels in check to avoid algae growth and calcium inhibition, but also try not to make the aquarium too “sterile”.