I sugest an oto catfish, which can fit comfortably in a 10 gallon, and from what i have heard, get along great with bettas. I have never owned one, but i love them! They are algae eaters, but you should also consider some blanched veggies or algae wafers. They also get up to 5 cm, so your betta should leave the oto catfish alone, and the oto catfish should leave your betta alone, too.
Last edited by FishFriend9292; 11-24-2012 at 08:48 AM.