I disagree with this heavily. I have 3 Angels in a mixed reef and it’s nowhere near 400 Gallons. It’s - 5’x2’x2’ 180G tank.
I don’t do anything special. I don’t feed more, I don’t just keep huge colonies. I just don’t keep certain coral I know they’ll eat. All angels are reef safe, they will just nip at specific coral - avoid those coral and you’re fine. Don’t keep;
- Zoas
- Acans/Micromussa
- Scolys/Trachys
Anything fleshy tends to be a no go.
I do however keep;
- Mushrooms
- Leathers
- Hammers
- Frogspawn
- Torches
- Various Acros
- Montis
- Gorgonians
- Bubbles
- Gonis
- Duncans
All healthy & happy with the angels.