anything over 82* is too much IMO unless your fish are sick. Waste of electricity.. I keep my tanks between 77-82*. On the warmer side when I'm trying to get stuff to breed. The only time I go over 82* is when my fish have ick or infections and even then I won't go past 84*. The only time I go lower is in my convict tanks when I don't want them to breed. I just take the heaters off and the tanks go down to 72-75*.