Aggression issues don't usually ramp up till the fish reach sexual maturity and start pairing off and claiming territories.
Your idea of mixing incompatible species really isn't anything new or cutting edge, most new fishkeepers do it until they learn better.
Lol I was waiting to be trolled on this site I figured it would be sooner. jeta, while I respect your opinion, I'll continue to do it my way. I will not learn better as you phrased it. (very patronizing and condescending, thought we were all friends here) I've had my big Jack for over 3 years, I'm sure sexual maturity has been reached. it was about 8 inches big in a 10 gal tank for months at my lfs until I rescued him. It doesnt claim any particular spot, and is probably my most passive fish I have. The only pair I have are the Johanni's and I probably will move them out for breeding purposes. I also have various species from different lakes but it works for me. besides you are speaking of situations that happen in any Cichlid environment. Incompatible is a relative term. peta as well as many naturalists would probably argue that we shouldn't house any species of fish in any tank. they are incompatible with living in a glass box. I'm not trying to be new or cutting edge. I simply like certain fish. Now if I thought one was being bullied or an issue did arise, Id have my net in there as fast as I could to relocate or rehome the fish.