I currently have a 55g with 3 smaller angels. I had 4 but one died, due to a poor quality fish I want to say. He stayed considerably smaller than the rest.

My local Walmart has had the most beautiful angelfish I've seen in a while now for almost a month. It's solid black with white bottom fins. Would it be safe to rescue him with these current 3, or should I get 2 more, or just ditch the idea all together?

I wanted this to tank to eventually be a discus tank but I don't think that will work.

I have a separate 20g tank running with 1 male sword and 1 female gbr. If aggression arose this would be too small for an angel right?