Planted Tank Guru
Join Date: Dec 2017
Location: Elk Grove, California
You could do a confirmed pair of Angelfish in a 40 breeder just fine. But, one Angel Fish ( while Angel fish are not necessarily gregarious and needing their own kind like many cichlids) will be a pretty dull aquarium for you and the fish. It would be better to see the interaction between a male and female pair than a lone Angel by itself.
So, sure, you can do a lone angel-- but, who would want to.
You could also, along with the Angel pair, do the two pair of dwarf cichlids providing their is adequate cover with plants, rock, and driftwood. Cichlids need their space to defend nd retreat to when needed.
The otos would be fine.
Schoolers like cardinals and rummy-nose?- maybe.
Depends on the inclination of the Angelfish. Cichlids being cichlids.