I don't see any reason to control temperature range as tight as one degree difference as my Apex is doing right now. So I am considering a change in my Apex settings. My house temperature is set to 78 most of the time in the summer. We occasionally lower it to 77. My tank room temperature, which is measured separately near the ceiling, swings between 80 and 82 primarily due to the old T5 fixture on my fresh water tank, which generates a lot of heat amazingly.
In my old house my 180 was in a west facing room, and my temperature in winter used to swing gradually between 78 and 74 (or even down to 72 on some real cold nights) under metal halide lamps and one under rated heater (150W). I did not see any ill effect. In summer time, my temperature in late afternoon went up to 82 with two fans blowing constantly at a high speed, but I did not see any ill effect. As a matter of fact, my corals used to grow faster in summer.
I got the feeling that corals are durable enough to take a few degree change as long as the change is very slow. I read a posting by Dr. Ron Shimek several years ago about this very issue. He was in the opinion that corals that are kept in the environment tightly controlled and never saw any temp swing did not take any big temp swing easily unlike those on natural reefs. Another researcher mentioned about a much larger temperature gradient in nature and recommended against keeping a constant temperature. I recall both Dr. Shimek and the researcher did a lot of field work on coral reefs in nature.
