The two species I mentioned are in the acara family. Well, given the number of species that get reclassified at one point or another, they might NOW be in a different family, but at least they USED to be acaras. In any case you can find a lot of information about them under the names I gave.
However, I should note that they are much smaller than the rest of the species, and that is what you would need for a tank as small as a 20 gallon. Not as small as dwarf cichlids, but much smaller than the average acara.