how about some convicts too?
Please tell me you don't mean "as well" !? :-(
You could keep any of the following Tanganyikan shell dwellers in a 20L, I've given a suggested starting ratio of males and females:-
Lamprologus multifasciatus (2 pairs or 1m 3-4f)
Lamprologus brevis (2-3 pairs)
Lamprologus similis (2-3 pairs)
Lamprologus ocellatus, speciosus, meleagris (2m 3-4f)
Lepidiolamprologus hecqui, meeli, boulengeri (1 pair)
Altolamprologus compressiceps Sumbu dwarf (1-2 pairs)
Neolamprologus caudopunctatus (1-2 pairs)
None of the above have blue/yellow stripes, if you're meaning tretocephalus, sexfasciatus or frontosa forget it.