Keeping angels in a reef, if the reef is well matured with lots of undergrowth, the damage from an angel is limited...especially a small one. I raised a tiny infant Imperator in an 18 gallon reef with lots of undergrowth and the polyps on top did get nibbled on, but not so much. They were able to recover or replace themselves. She was more interested in the sponges and algae growing under the rocks. May need to be a bit more attentive to the types of coral housed. Xenia would certainly get picked on and polyps and mushrooms should be in decent sized colonies. Not fragged. SPS
coral is of little concern because angels prefer the softies.
I know someone who has this huge reef...300 gallon. Has had it for many years. It's largely a SPS
tank with some anemones as well. He has 7 different species of large angels in this tank and has had them for as long as he's had the tank living together peacefully, well fed and without destroying the tank. He's also had boxfish and an orange spot file fish without any ill affects. The orange spot file actually lived well for up to 6 years. It's hard enough to get them to live for a few months...and he ate flake food...wow. Very unusal, but it did have free access to the acropora they require...and he didn't lose anything due to it's predation. He's got himself a very working tank...LOL. It's beautiful!!
We, as a people, know so much more about outer space than we do about our own oceans. This lack of knowledge can very well spell the dangers that lay in wait for us.
The oceans surely would swallow us before a rock comes down to smite the planet of it's life.