When it comes to space requirements, a few of the smaller species are actually suitable choices for small reef tanks less than 30-40 gallons in volume, as long as the tank isn’t occupied by too many other fishes. Having more space to move around is always better than less, though, and having plenty of shelter is very important for dwarf angels, too. These diminutive fishes are preyed upon by larger predatory fishes on the reef, and are thus somewhat skittish at times and like to have ample hiding places to duck into. So, there’s another good reason to have plenty of live rock in an aquarium housing a dwarf angel, as it can be arranged in ways that create spaces for these and other fishes to swim through, and to hide in when they feel the need. Likewise, any non-reef hobbyist who doesn’t use live rock should still provide them with plenty of other sorts of decorations and suitable refuges.
As far as compatibility with other fishes goes, many (but certainly not all) dwarf angels get along fine with other sorts of fishes (that won’t eat them), such as tangs, wrasses, gobies and blennies. The same cannot be said, however, for their compatibility with other dwarf angels. As always, every individual fish of a given species can have a distinct personality, with some being more peaceful than others but, for the most part, trying to keep more than one dwarf angel in a small aquarium is a bad idea. They tend to be quite territorial and, in most cases, two or more dwarf angels will not get along at all. This is especially true if more than one individual of the same species are kept together, which is often impossible in most tanks. They usually wind up endlessly harassing each other.