Small fish, you could get Apistogrammas, Pelvicachromis, Nannochromis, or small species of Geophagus or Microgeophagus (rams). These would all be fine in soft slightly acid water (GH below 150ppm and pH below 7.0).
You could have a pair or trio (1 male & 2 females) in the tank and they would have room to breed and look after the young. A single pr usually gives better results.
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Fish like Cyprichromis, Paracyprichromis, Julidochromis, Lamprologus, Neolamprologus, Aulonocara are from the Rift Lakes in Africa and need hard water (350ppm+) with a high pH (7.6-8.6).
The Cyprichromis and Paracyprichromis are schooling fish they need to be kept in groups of at least 6 (preferably 10) or more.
Julidochromis can be kept in pairs or several pairs.
Some Lamprologus and Neolamprologus should only be kept in pairs but others can be kept in small groups of 6-10.
Aulonocaras grow to 4-5 inches and you could have a couple of males and some females. The males are quite nicely coloured.