I have an Aqueon 300w heater in my 55g. Recently I have had to move the temp up to 83-85 degrees to combat an ich scare. Now that I have beaten the scare I turned the heater back down. The heater is at its lowest setting but I can't get the temperature to drop below 81 degrees. I bought brand new digital thermometers a couple weeks ago so I don't it is the thermometer. Don't know if the heater is malfunctioning or it is compensating for the New England winter and temp changes in home.