Who Gives A Fish Forums

Plants are a great idea. Java Fern and Anubias are low-maintenance and provide good cover. Also, consider floating plants like Frogbit. They diffuse light and give the Betta a place to rest near the surface.

I agree with Koralin. The general rule is 1 inch of fish per gallon, but Bettas are territorial. Your tank is technically within limits, but the Betta's behavior is the real indicator. How often are you doing water changes? More fish means more waste, so you might need to up your maintenance game.