Betta problem

[Richer]

Little more info needed... is there a filter on this tank? Heater?

Contrary to what is commonly seen... bettas need normal filtration and a heater just like any other tropical fish. I would suspect that less than optimal water conditions is the cause of your betta's problem. If you want to run the tank without filtration, I would suggest doing 80-100% water changes at least once every other day... and to feed lightly (2-3 betta pellets a day).

-Richer