My expierience... Keep your angelfish smaller than your discus, they are far more aggressive than the discus when it comes to feeding and territory. I perfer to keep discus with discus. They seem to do much better this way. Also, keep small stingrays with your discus and angels. It (angels or discus) doesn't have to fit in their mouth, it just has to be able to fit under the disk of the ray. I have had many fish pinned and chewer up by rays, much more powerful fish than we are speaking of now (peacock bass, tinfoil barbs, midas cichlids, and so on). We had one that had a nack for chewing the heads of of fish. It can be done, but be ready to loose your small fish to the rays eventually.
