Another thing to consider with bettas in community tanks: if the filter creates much in the way of a current, your betta would be most unhappy. They like still water as their fins aren't built for fighting currents. I shudder to think about the time I gave this a try: after going to great lengths to create a "betta corner" in my 46-gal. away from the filter & sheltered by tall rocks & plants; the poor guy was pretty much thrown around by the current & never even found his betta corner; he was back in his 2-gal tank within 5 minutes.