Mixing new and old worlds can work but often doesn't. Water parameters have very little to with it as most old world cichlids are farm raised and have evolved to no longer need the ph levels required of their wild relatives. In my experience it has more to do with language. What I mean by that is they speak a different "fish" language. When new world cichlids have conflict they have a way of determining dominance. Once that is established it can, depending on tank size be the end of the problem. When an old world cichlid is in a conflict with a new world, often the communication between the fish is misread and leads to greater conflict down the road. In addition, some old worlds are very quick and the new worlds end up with tattered fins. In my 240 I have a Buttikoferri that does great with new worlds. So who knows if it will work. I have had a 4 inch bumblee shred a 14 inch flowerhorn. Water parameters should not be an issue so long as you have good water quality and a constant PH.