I would recommend a 55gal or larger. Overstocking will reduce agression, but will also increase your involvement in maintenance (weekly water changes ideal). Heavy filtration (twice the usual manufacturers recommendation for their filters is a good guide, IE an ac110 on a 55gal), you also need to buffer the water to a high Ph, you can do this with chemical buffers, or ideally with crushed coral (aragonite) or the like. Also, Mbuna like salt. It is best to use salt specifically for African cichlids (because it contains the trace elements they need to thrive) but not essential. I have heard of some people using a combination of regular (Mortons) salt and baking Powder(Or soda?) but ask someone else about that because I don't know the combination. Lastly, you want LOTS of hiding places, there will be dominant fish in your group and the less dominant ones will want places to escape their chasers. Good luck! they are by far the most entertaining fish in the hobby!! (in my op)