120 liters is a bit small for african cichlids, unless alone. It's also extremely important to know the species of the fish that you have, as this alone can determine possible tankmates.
I believe BJC787 tried to explain a couple of times that the tank currently has no fish, just looking for something to put in it.
At 31 gal, your tank is too small for any of the Lake Malawi species, however, Lake Tanganikya is your answer. There are several smaller species that would fit quite nicely, especially any of the shell dwellers. http/www.cichlid-forum.com/articles/shelldweller_corner.php
I know this is a African cichlid topic but you could always try South American cichlids where there are a lot of dwarf cichlids suitable for your size tank. The Cockatoo Dwarf cichlid is my personal favorite which I hope to keep once I've upgraded my tank and have a spare 125L for breeding them
Tanganyika shell dwellers are really interesting too though