My betta has been with us for over a month now but has had no heater. His water is at 72. Everything I've read says he'll be happier with one. If I put one in, will it adjust too quickly for him? Or will he adjust with it? I've bought two mini heaters for him but they're both sitting on my desk until I know what's best. As he's in a 3g, I found the Aqueon Mini Heater 10w and the Tetra Submersible 50w. Reviews on the Aqueon say it doesn't shut off at the preset temp. The Tetra had much better reviews. Neither have adjustable temps. Both are supposed to stay around 76-80F.