Over the years I have kept Potter's, Coral Beauty, Flameback, Cherub, Flame, and I currently have a Bicolor( hey, I like dwarf Angels) . Through my experience and like Jason2459 says...as long as they are kept well fed with algae they will be fine. Keeping them well fed IMO drastically reduces there urge to nip at corals. I never had issues with any of mine chowing on corals but every fish is different. With your size tank you should be ok keeping 1 or 2 even. I do though recommend not keeping a pair of DA in a tank smaller than 100 gallons but there are others on here who have had good success with doing it. Again, every DA is different. My bicolor is no problem at all in my tank and IMO is the most colorful of them all. I will say this though about him...he doesn't take too kindly to other fish with similar coloration as his but with time he has cooled down. As long as your tank has plenty of rock work with well established algae growth then you can keep whichever species you decide on. Hope this helps.