I hate to admit it, but a 3-4 years ago, I actually forgot to plug the heaters back in after changing the water in my 55G FW tank. The temp dropped 10 degrees before I noticed it...Luckily everything survived, but I was a little nervous for a few days. :eek1: Clown loaches are noted for being a little finnicky about water parameters, but they were just fine.
Fortunately, in my reef, it would be hard to notice the main pumps not being on, which seems to provide for most of my heating needs. I don't think the tank would drop below 75-77 in the winter even if I turned the heaters off (I keep it at 80).