The only time I use heater in freshwater tank is combat ich, other than that I run my tank as room temp even in winter the water temp drop around 60F~62F and my fish are doing fine and seem don't care about temp as long it rise and drop in timely manner. The only tank that I keeping heater in winter at 76F is my saltwater reef tank cause saltwater live stock are more sensitive to temp change, I'm quite sure they will be fine too but I'm not risking a few thousand bucks for experiment 