All male tank is fairly common, both for CA/SA and African cichlids. By keeping out females, you also keep out aggression from breeding, because even peaceful cichlids get aggressive in breeding time. Keeping all females may not work to reduce aggression from breeding, because females can lay eggs by themselves or pair up with other females. I have never heard of two males pair up. Moreover, females are generally less colorful than males, so what's the point of keeping all female tank except for breeders.