A 20H is pretty limited with regard to cichlids (at least long term). I don't like to keep pairs of cons, Cryptoheros or the like in a 2' tank (at least without a divider handy) - too much chance of the female getting offed...
I don't want folks to get the impression that goodeids are bad fish to keep. Just the contrary.
Goodeids run the spectrum from mean as heck (e.g. Ilyodon) to really peaceful (e.g. Chaplicthys, Xenoteca, Atenaeobus toweri) and somewhere in between (e.g. Ameca, Goodea, Chracodon).
As mean as they are to other fish (and I keep mine with medium-sized CA cichlids grow outs), Ilyodon (furcidens, xantusi, whitei, etc.) are relatively peaceful with each other and almost never eat their fry. I had a 2'x2'x1' dedicated to them at one time... started with 2 pairs and had bunches after a few months. I added some 2-3" ones to a big tank of mbuna and they dominated the top layer of the tank.
Matt