Ask Marc: Betta Fish
I recently bought a Betta fish. How often do I have to clean its bowl?
The more often you clean its bowl, the happier the fish will be! Just about all Betta fish sold in the United States are raised in Thailand, and breeders there generally change the bowl water three times a day. In your home, changing the water AT LEAST every other day would be ideal. Just be sure the new water is the same temperature as the water in the bowl.
Keep a bottle of water near the fish bowl and use that water when replacing the old water in the bowl. It will be free of chlorine and exactly the same air temperature as the original water.