Crush coral as gravel will help bring up ph, so will holey rock and maybe you can try the home ph buffer mix thats in the library as well. I would stay away from ph buffers from the stores they can get pretty expensive. You dont have to hit 8 ph mbuna will do just fine at mid 7.5.
My PH is 7.6 and my peacock cichlids are doing just fine. But the OP said his is under 7, thats pretty low.
*** never wanted to get the perfect 8.2 but some say you can add crushed coral to your filter too to raise it...but youll probably need a big filter, not really sure. Like everyone said though...raise is slowly.
I have a large piece of driftwood in a rubbermaid container (trying to get the tannins out) and *** been using a&h baking soda to raise it. You can also use soda ash if you have that on hand.