Despite everything else that you may have read everywhere, 82-84 is the acceptable range for reef tanks. It represents an average temperature in surface water (down to 160 feet I believe) of most of the coral reefs in the world. I have a chiller that kicks on at 82 and off at 80 only because I have been stuck in the land of 78 degrees for too many years. When I increased the chiller settings from 78 to 80 everything, including the fish, seemed happier.