Putting a male betta in a 20g is a pretty bad idea. It would server perfectly for a community tank and by putting in a betta, not only are you giving it way more space than it needs, you are also making the tank unable to be used as a community tank, UNLESS he gets a divider.
Putting a male betta in a 20g is a pretty bad idea. It would server perfectly for a community tank and by putting in a betta, not only are you giving it way more space than it needs, you are also making the tank unable to be used as a community tank, UNLESS he gets a divider.