You're doing well to keep the S. Americans and Africans seperate, the Africans are more agressive and would kill the S. Americans. I had a Melanochromis Auratus that kept harassing the rest of the cichlids to death. I finally put him in a tank with a ruby shark and a clown pleco. The ruby was bigger than the auratus and could stand his ground. They developed a healthy respect for each other.
I have found that Africans survive better in a crowded tank. It gives the alpha fish lots of targets so the inevitable trauma and stress is spread out over many fish instead of focusing on just a few. It seems the alpha tires his self out before causing serious harm to any one fish, at least most of the time, and the tank seems more comfortable as a result.
Yeah I have my Africans and South Americans separated.
That's why I want to buy more Africans, my alpha male has about 4 fish he really likes to harrass. And i feel bad, So i really want to stock up my tank to a healthy number.
And i know in the wild, africans live in very cichlid dense places
When I add cichlids to an established tank I never add just one, I always add 3 at least and 4 is even better. It seems that when you just add 1 the whole tank focuses on that lone newcomer but 4 or more is just too many targets. It really livens up the tank too.
Man I love Cichlids, they have interesting personalities.