It can also depend on the animals you keep. Like Dave, I keep mine from 77.5-78 Range. In Ronald Shimek's Aquarium Frontier's On-Line Magazine article What are Natural Reef Salinities and Temperatures...Really...and Does It Matter?, he makes the point that the corals you have in your tank come from many different ocean water temperatures ranging from 72 degrees up to about 92 degrees. He states that "Maintaining a tank in the upper 70 degree Fahrenheit (24 to 26 degrees Celsius) range will stress any reef inhabitants from the central Indo-Pacific, as it is too cold. And, because this is near the upper limits for subtropical organisms, it will stress them as well. It would be better for all concerned if aquarists concentrated their efforts on maintaining separate systems for organisms from geographically disparate areas." Knowing what kind of animals you have and where they come from play an important part in deciding what is the best tank temperature for your aquarium.