#betta bloating

So I've been having some issues with my betta. He is almost always bloated, even after a week long fast. I have stopped feeding pellet food all together and keep him on blood worms and brine shrimp. I have done epsom soaks and treated with kenaplex and metroplex while on the fast. His condition will improve, but by next afternoon he is bloated and floating again. Water temperature is at 82 degrees Fahrenheit and receives changes. I'm really starting to worry because his fins have started fraying as if he's tail biting. What's up with my betta?