I'm going to disagree with many of the posters here. 4 angels in a 55 is a recipe for lots of nipping. even more so if the angels pair and try to breed. I think you may be ok with 2, but 4 is a little crowded for them. I think the rainbows will be fine with them, as long as you don't have the dwarf variety, that can be small enough to fit in the mouths of the full grown angels.