i went WAY overboard on my heaters i got 2 400 watt heaters in my 125 i had no idea what to get when i got them and i jsut looked at the package and they said like 80-100 gal. so i said to myself "self, you are going to need two of those big MOFOs" then i set the tank up and turn them on and the heaters are set at 76 and the tank wante to stay at 82 so i went off the deep end but hey at least i know what to buy next time lol