There are many, different Cichlids that do well in smaller tanks, they are called Dwarf Cichlids. They are found in South America, and Africa; in the lakes and the rivers. Some of my favorite dwarfs are Julidochromis from Lake Tanganyika in East Africa, there is also a several "Lamprologus" that they call Shell Dwellers from that Lake, they are all small, some only reach 5 cm. (2") as mature adults. Keeping these types of fish would require adding a water conditioner to increase your pH. Then there are many other dwarf Cichlids from the rivers of Africa, this would include kribs. From South America their are is a whole family called Apistogramma, all of these fish have nice color I think! Since your water is quite soft, and if you don't want to deal with the water conditioners you should be looking at South American, and African Riverine, type species. Look up Apistogramma and Pelvicachromis. Electric blue johanni (Melanochromis maingano) and Labeotropheus trewavasae, are both very colorful species, but they are not going to go in your size of tank. They are more of group fish, they are harem breeders, one male to many females, and they really need a larger tank to do them justice.