What size of tank? What do you have in there now?
I find having a bubbler in the background, not only adds a neat soft look to the tank (I use an adjustable valve to moderate the amount) also helps with the CO2. Live plants also help aid in getting the "good stuff" to other fish, who, unlike bettas, are in higher demand of oxygen.
Personally I would worry more about an overstocked tank not getting what they need.