Viv's not wrong. Bettas are a tropical fish. Air temperature is different than water temperature. It's a few degrees cooler. In Thailand, the temp stays 85 and above year round. So your water temp. should mimic that. 78-82 is right where you want to be, without fluctuation. I keep a constant water temp. of 80 degrees even know my room temp. here in Philadelphia is between 68-74.