Look, you need to give us numbers, not just tell us water params are "ok". Just because the guy that does your tank said it wasn't pH shock doesn't mean squat. You need to know the pH of the place your getting the fish from and then where you are. Sounds like you have malawis (well had), convicts are nasty little central american cichlids, just not a mix for water reasons and aggression issues. If that guy is telling you they will be fine together, its time you look for someone else to do your tank. He certainly is not a "pro".You still did not anwser our question about what size the tank is, also its not the convicts if the ones dying aren't all torn up, they certainly aren't dying from fear of the convicts.