I have 2 heaters in my big community tank. There was no option for me because they just don't make 500 watt heaters. The rest of my smaller tanks have either a single heater or none at all. I keep a lot of goodeids that like their water around room temperature and many of them are healthier if you let their temperature move around with the time of day and the season. Those tanks just don't need a heater and I don't need the power bill for a fish that could care less.