I have a 1o gallon tank with 100W Aqueon Pro heater. The reason for the 100W heater is that the difference between the room and tank temperature (for the fish I had) was about 18-20F. Now, I would like to get some White Cloud Mountain Minnows which like cooler temperatures. The room temp is still too low for them to have a tank without a heater but wouldn't the 100W one be too big and cause some discomfort for the WCMMs even when it cycles on and off? I am assuming that when the heater is on, it produces full 100W of power unless I am mistaken. The only other heater I have is a small 25W Cobalt Neo-Therm which is way to small for a 10 gallon.