my sister had 3 betas. they died bc she wasnt using filtered water. anyway, she got 6 fish recently. a sucker fish (lasted a day bc the water was too clean), two angelfish (one of which ate all the other fish in the tank), two transparent glowing fish (eaten by the angelfish), one fancy fish with a flippy tail (also eaten by the angelfish). so two weeks into the endeavor, she had a ten gallon tank with one resident fish.