The black calvus is from Lake Tanganyika and is a rift species. Calvus are somewhat shy. You can try other Tanganyikas like leleupi, brichardi, or julidichromis. There are also a number of shell dwellers that remain fairly small. You may be able to get away with some of the less agressive peacock cichlids from Malawi or maybe even a demasoni, which stays small. If you want to spend a little more you could try some small Frontosa.