<a href=showthread.php?s=&postid=8970959#post8970959 target=_blank>Originally posted</a> by critterkeeper
I live in Tampa and my tank STAYS between 82-84 year-round. I trust my AC, and keep a couple of big frozen tupperware things full of water in the freezer, just in case I ever need to drop the temp a couple of degrees. I have a couple of extra fans for any unforseen emergencies, too...
The advantage of a high temp is that cold-blooded organisms' metabolic rate is tied directly to environmental temp. Higher temps will lead to faster growth for corals and for clams - but only up to a threshold of about 86-88 degrees. Another advantage (of course) is not paying for/running a chiller, and not keeping the AC lower than I want to have it for myself, just to keep the tank cooler.
Reefkoi, 84 is close to 86, and my guess would be that if you saw widespread losses at 84 - the thermometer was off a couple of degrees and the tank was really higher than what it read. OR, it could have been due to low oxygen levels. When temps go up, oxygen concentration goes down. As long as there is LOTS of circulation and a rolling water surface - no problem. But if temps go up and ciculation is too low, oxygen can drop too much...