Angels prefer a tank height of 18 inches minimum. A portion of space can be planted with Echinodorus sp. or the eleocharis or vallisnerias. They like to hide amongst tall plants. I agree with krytan. 55g should be your minimum. Angels have the tendency to reach 6 inches body diameter often minus the tail. Leave an open space area in the front. Adding slates and driftwood is not a bad idea at all. If you wish to keep other fish, please make sure none are too small to be eaten by the angelfish. Try rummy-nose tetras, lemon tetras, diamond tetras, black phantom tetras, hatchets, corydoras and small species of plecos. Keep temperature steady at 78 degrees Fahrenheit.