I used to be really concerned about constants in my tank and temp was very important. I calculated it well so that my tank would never swing more than 1 degree through the use of a fan on a timer. That fan has since broken and I no longer use it. My tank now swings from 80-84 by the time the lights go out. I have a few sps and softies and all my corals seem to actually be doing better since the fan broke. I don't have any scientific data or anything but "my" tank so far seems to handle, what I consider a large swing, very well.