They'll be fine unless you're talking about some WC, notoriously delicate rift lake cichlids. I've mixed africans and centrals on numerous occassions with much success. I have F1 Telmatochromis dhonti breeding in a tank with a school of Exodon paradoxus and a few small pike cichlids (they've killed jsut about everything else I've tried but pretty much leave the pikes to their own business as longa s they don't get too close to the breeding cave), all of this in tap water with a pH of 7.2.
If you're buying captive bred fish, water conditions start to matter less and less, and when you're talking the little farm bred cichlids that most lfs stock, it matters even less. Most lfs keep all their fish in the same water conditions (they use one or 2 central filtration systems that pumps the same water through all the tanks).
Furthermore, many cichlids (africans) are bred on farms in large vats or ponds using local, untreated water of unknown conditions. If you look in the "assorted africans" tanks, you can usually spot a hybrid or 2 in there... if the africans weren't responding well to the water conditions, why were they breeding? I've seen centrals (cons, jds, small rds) that came mixed in asst african shipments, more than likely jumped over from a neighbouring pond. They're doing just fine as well, eating, displaying colours, and often holed up in a corner defending against maurading africans.
I can only recall 2 instances I treated water at my house to change the pH: blackwater extract to get WC altum angels to spawn, which they did, and continued to even after i ran out of it and went back to normal 7.2 tapwater, and baking soda for a rather pricey group of WC Petrochromis, which I ended up selling not too long after due to aggression problems amongst the group.
As I said, providing the fish are compatible temperment wise, I really don't see a problem unless you're trying to breed WC, delicate species.
If you're buying captive bred fish, water conditions start to matter less and less, and when you're talking the little farm bred cichlids that most lfs stock, it matters even less. Most lfs keep all their fish in the same water conditions (they use one or 2 central filtration systems that pumps the same water through all the tanks).
Furthermore, many cichlids (africans) are bred on farms in large vats or ponds using local, untreated water of unknown conditions. If you look in the "assorted africans" tanks, you can usually spot a hybrid or 2 in there... if the africans weren't responding well to the water conditions, why were they breeding? I've seen centrals (cons, jds, small rds) that came mixed in asst african shipments, more than likely jumped over from a neighbouring pond. They're doing just fine as well, eating, displaying colours, and often holed up in a corner defending against maurading africans.
I can only recall 2 instances I treated water at my house to change the pH: blackwater extract to get WC altum angels to spawn, which they did, and continued to even after i ran out of it and went back to normal 7.2 tapwater, and baking soda for a rather pricey group of WC Petrochromis, which I ended up selling not too long after due to aggression problems amongst the group.
As I said, providing the fish are compatible temperment wise, I really don't see a problem unless you're trying to breed WC, delicate species.
Maybe I should have been more specific and noted that either care be taken that the dietary requirements of all inhabitants be met, or that the more omnivorous species of mbuna (melanochromis, cyanotilapia etc.) be used. 
