Hello! I am entirely new to betta keeping! Yesterday, I just bought my male betta fish (Delta tail male). Currently, I have him in a 1.5 gallon tank with gravel, a live plant, and a floating log (with a hole in the middle to hide). I bought him last night. This morning, I figured I'd feed him. The lady at the pet store said to feed him every other day, and feed him 6 pellets. So this morning, I decided to feed him. I started with one pellet to see if he ate them, but he's not. I tried again in the afternoon, and he's still not eating. What should I do? The water is at 72 degrees, but I'm considering buying a heater...If I do buy a heater, which one should I buy?