Orion said:
In a big enough tank both rams and kribs could co-exist and even breed. But a 20 gallon isn't anywhere near large enough.
Couldn't be truer. The main problem with mixing Africans and fish from other continents is reuirements of the water's chemisty.
Quite generally:
South American = soft water
African = hard
Since what most people think of when they hear "African cichlid" are those of the alkaline rift lakes this would make sense. This absolutely does not apply to many of the non-rift lake species. Like kribs. Which come from soft water rivers in West Africa. In a larger tank rams and kribs could certainly get along.
But the tank being stocked does not have the capacity to hold more than one breeding pair of such fish.
If you want a colorful community you'll have to realize that larger fish are out of the question. The bigger they get the less you can keep and I'd say 5" should be the maximum adult size of a fish you decide to keep in there. A pair of kribs
or a pair of rams would fit nicely in there as would a pair of one of the more popular Apistogramma like A. cacatuoides, A. macmasteri or A. agasizzii. Another soft-water loving dwarf African cichlid that would do nicely is Anomalochromis thomasi and for South American again is Nannacara anomala. The charming Laetacara curviceps or dorsigera might be worth looking into as well.
Any of these, only as adults (possibly 3 for A. cacatuoides) along with a nice school of smaller tetras and possibly a small group of bottomdwellers like khuli loaches or smaller Corydoras catfish (like C. panda) would max pleasantly max out a 20gal tank.
If you'd like to opt for a pair only tank (2 breeding fish, no tankmates) look into the fairy cichlids of Lake Tanganyika.
Neolamprologus brichardi, pulcher, helianthus, gracilis, marunguesnsis.
They are becoming much more popular and a perfect pair inhabitant of Neolamprologus brichardi are actually not too hard to find now-a-days. Why only a pair? They get to a considerable size (4-6") and are very aggressive. But they are absolutely stunning.