Yeah, my bettas would also eat the entire food jar if they could. :) They are little aquatic pigs :)) Unfortunately overfeeding leads to a lot of nasty things for bettas, so prevention is very important for a happy and healthy fish. I would say you gave him too much. The amount of food depends on the size of the pellets that you feed him. Anyway, you have to feed him small portions of food, twice per day being the best, instead of one. Keep in mind that betta's stomach is about the size of its eye.