You can have up to six angelfish in a 55-gallon tank. An adult angelfish requires about ten gallons of water to live comfortably. Lack of swimming space and an overcrowded tank can result in territorial fights.
If you intend to keep other fish species as tankmates for the angelfish, you’ll need to factor those fish and their own needs into the equation as well.
Additionally, if you’re a novice fishkeeper, starting with two angelfish in a 55-gallon tank is recommended. After you’re comfortable taking care of them, you can start introducing more angelfish into the tank.