Just one other species? You could get away with a couple more in a 55. Any one of these would work.
Pseudotropheus sp. "acei"
Metriaclima sp. "Msobo"
Metriaclima estherae
Iodotropheus sprengerae
Metriaclima callainos
Pseudotropheus polit
Pseudotropheus socolofi
Pseudotropheus sp. "acei"
Metriaclima sp. "Msobo"
Metriaclima estherae
Iodotropheus sprengerae
Metriaclima callainos
Pseudotropheus polit
Pseudotropheus socolofi