nvan2 said:Most likley theres nothing wronge with him... bettas are very very hardy fish. You might want to not change the water as much,or take less out at a time. Technically bettas can go months in a 1 gallon fish bowl without ever cleaning it, although thats not really nice to the fish.
If there is, hes probably loosing some color because he is stressed for some reason. Depending on when you set your tank up, there could be high amonia or nitrites. take it to the fish store and have them test it.
I would do the opposite. I would change the water more not less. NO fish, not even bettas, can go months in any bowl/tank/container without ever cleaning it.