12 africans in 55 gal.

yeah i know what you mean i have 17 in 100 gal i tried to give some to a friend i ended up getting my fish back to restore the balance....you could try and wait it out they just need to get the ranks figured out.......my fish almost killed each other so i brought mine back

african Mbuna are polygamous which means that males will try to spawn with all the females of the same species and others that look like them. to reduce this spawning aggression, Mbuna should be kept in a sexual ratio of one male together with 4 females of the same species. other Mbuna in the tank should be a different color and general shape so as to not be confused with other Mbuna of a different species. you may have removed two females and offset a sexual ratio that was apparently working.

too, Africans need alot of rock work in the tank; floor to top with lots of nooks, crannies and caves which provide at least one cave per female and male.

It really depends on what your goals are. In my mbuna breeding tanks, I usually only have a couple, diverse species in the ratios that liv2padl suggested, that are unlikely to interbreed, or a species only tank. Now for my mbuna show tanks that are essentially only males I stock MUCH heavier with great filitration, a ton of rock work and frequent water changes. In my 90g mixed mbuna tank, I have about 35 + fish. In a 55g, if it were primarily mixed males, I would house 15-20, again with the set up mentioned above -rockwork, heavy filtration, water changes. These are the ratios that have worked for me for 25 years of cichlid keeping, and the way that other cichlid breeders I know do it as well.