what is a good betta fish tank size? I recommend 3.5 gallons and up, and have had a lot of success and had some very happy bettas in 3.5 gallon tanks, though this is the smallest I would recommend, and you must also consider the shape of the tank as well. A tall column shaped 3.5 gallon tank will not have a sufficient amount of surface area, and will not be a good choice. With a 3.5 gallon tank, decorating the aquarium can be a challenge. Betta's love to have good hiding places, but you also must not "crowd" the tank too much either, which can be tough with the small footprint of a
3.5 gallon betta tank.planted tank is always a better option.