I have not kept any myself, but from those I know who have, the biggest tank you can supply. I'd say 75g absolute min and that would be with no other fish or crustaceans in it. They, especially the females, get big, like 6" including tail. Hold up a $1 bill - that's the size they get. They are highly aggressive and territorial. Every single person has said anything they put in the tank, like their hand for instance..., is attacked. Considering my much smaller A. melanopus mama sometimes attacked and could almost draw blood, I'd think three of four times before putting bare hands in with a maroon pair. And my clowns were in a 120g tank.
Not that any of this should discourage you if that's what you want, just know what you're getting into. Good luck.