Hey all new question lol. What size heater is good for a 10 gallon? I have a 100w that came with this aquaclear pack thing i got at the lfs. Then there is the 25w in his 5.5 right now. Im pretty sure the 25w wont be enough to heat a 10 gallon,else i have to turn it up even more to get it to 80. I had to turn it up as is to warm up the 5.5,its like a few degrees off. I dunno if lfs will take back the 100 so i can get a 50 instead. But if a 100 is fine,then ill use it. It has a temp dial on it. Id like to hear what yall think before i open the package and cant take it back lol. Thanks again!