Ok so I have been using a 200w Aqueon pro heater in my 55 gallon for 6 months now and it is awesome. It has been really tested this winter. The temps where I live this winter have been either single digit's or negative. Had an issue with my furnace the other night and the temp in the house was 55 degrees. That 200W heater maintained a 79 degree temp in my tank without any issues. I didn't turn it up its been set to 80 since I installed. I know a lot of people would think I need more watts but this thing performs flawlessly.. Kudos to Aqueon for a great product!!!!!