my green sunfish has developed white fuzz around his mouth and a few spots on body. I usually keep the water heated at about 73 deg F. But I unplugged the heater, and week later its sick. So what are the advantages of keeping it heated or not heated. It was heated for 6 months without a hitch, and I have a routine so nothing has changed except the removal of the heat. Is now 65 F or so. Other fish are fine as of now.