Hi
Have often heard of that but in my own experience the only thing that ever happened was they failed to turn on .lol
If you unplug it will defeat the purpose?? gary

Bettas are tropical fish, where the water easily reaches 80 degrees in their natural habitat. I have a 10 gallon tank with a heater constantly set on 85, and nothing's gone amiss. If you're worried about you fish dying, I suggest getting a bigger tank. That way, the heat distributes space.in a wider area instead of an intense heat in one small.

Best of luck, Kelsey

If you invest in a tank light, that usually heats the water enough. Or if you invest in a tank with a filter that has a hood and everything on it, I've found that the filter motor produces enough heat to keep the water at 80 without a heater. And if it inches past 80, all i have to do is open the lid for about 30 minutes and it's good to go for another day. 2.5 is a good size for a Betta - but the no filter thing concerns me. People don't realize how much happier their betta could be if they would just add a filter. You don't even have to run the filter all the time! Even running it for one day a week would be adequate to keep everything balanced and clean. But they CAN survive in a tank without a filter.. they just aren't as happy. They don't THRIVE.