It's a shame, in a way, that these fishes are caught and offered for sale to the hobbyist. Few can really properly house them.
If the fish is still in its juvenile form, they do well in smaller tanks (55s and larger). As they begin to lose their juv form and become young adults, they must be in a minimum of 180 gallon aquarium. A fully changed adult large Angel should be in a 300 gallon aquarium until they get to over 7" in size and then should be moved to a 500 gallon or larger aquarium.
A very alarming big percent of large Angels caught in their adult form, die before they are more than one year in captivity.