I have been maintaining my tank between 81 and 84 degrees, as this is the norm for upper water reef temps from the Indo-Pacific region. This from Eric Borneman's book:
"Although it has been recommended in the past that aquarium temperatures should be maintained between 24 and 27 degrees C (75 to 80 degrees F), the natural temperature of many Indo-Pacific reefs, especially in the shallow areas where most corals are collected, is higher than 27 degrees C (80 F)
It had always been assumed that temperatures lower than natural levels prevented the rapid growth of unsightly algal films on the aquarium glass and lessened the proliferation of problem hair algae. Recent trends favor maintaining somewhat more natural reef temperatures of 27-29 degrees C (80-84 degrees F) The reason behind this increase is that the entire metabolism of the tank is raised, including those of the microbial community, detritus-processing organisms, and herbivores. Furthermore, it is a more natural temperature for many reef animals. The increased rates of calcification at these temperatures should, therefore, not be offset by increasing algal growth, unless the system is mismanaged."