82 tops. Preferably slightly under 80 for most things. But yea, coral bleaching all over happens when temp remains above ideal for extended periods of time. If it stays that hot with heater off, run some fans over the surface of the water and against the sides. Unless you see the need to go for a chiller.
Keep in mind fans will increase evaporation rates. My tank is sitting at 78 degrees and seems off too a good start.
Display tank - 24g nano w/ softies/montipora
I run electrical appliances underwater and enjoy injecting things with Kalk filled syringes.