Mine runs between 81-84 just before the lights go out. Eric Borneman was some great insight into reef temps. Very few are at 78 apparentely. Most are a little higher. It does speed up metabolism of algae, but it also speeds up the metabolism of everything else in the tank as well. Anyway, I'm a lot like you guys, my lights dictate what the temp is. Any thoughts on a 3-4 degree fluctuation throughout the duration of the day? The corals appear happy? Would they be happier if it was exactly constant? Or this yet another anal thing that we all go through? Any thoughts?