it will eventually hurt the angels. try to give it back to the store, they may even let you trade it in. BN plecos are ok, common plecos get rather big and would need a bigger tank than yours i think. some of the inverts, shrimp and snails, can also be good i believe, but i don't know enough about them to really recommend anything. you can look through the fish profiles (second tab in across the blue bar at top) for more information. make sure you get something that can deal with the same water parameters as the angels (shouldn't be hard).