I keep mbuna like the ones you have, bloodline.
I'm normally not a fan of major pH adjustments, but that's really low for them. In the wild, they live at pH 8.2 or so and even though you probably have tank raised ones, they're still not going to be physiologically comfortable in acidic water. As rdd1952 says, get yourself some limestone rocks or some aragonite sand for the tank, or just add some crushed limestone or coral in a fabric bag (or pantyhose) to the filter. That will help buffer the water.
I regularly perform 50% water changes with these fish, including tiny fry. The only difference I notice afterward is that they're more active due to the highly oxygenated water. Mbuna are hardy and resilient fish.
Granted, you'd need to slowly adjust it up, but once you'd done so, you can add baking soda (which costs next to nothing) every water change to keep your water stable and at 8.2, 1 tsp/5 gallons. That's what I do at least...
Just some thoughts...