Aregentea are nasty. I'm starting to think they do all their violence when the lights go out. In a Vieja tank, they own the night.
Heterospilus are pretty laid back and grow really slow. From what i understamd they are on the smaller side (less than 10 inches) mine doesnt bother anyone infact usually gets picked on.
Also have zonatus and had argentea in the past wouldnt even try to mix them with other cichlids.
Post some pics later
not gonna have space till I get the 125 in....