I agree with BettaFishMommy that the angel fish likely need more room. They get to be 6", and they need a tall tank (at least 20" tall I believe), and they will need more room than a 20g soon. I think cories would do well, and many places sell them. But, they need to be in a group of at least 5 for better health and less stress, so they need more room than 20g also. Keep in mind that you will also have to feed them more than just what hits the bottom from feeding the angels.