The "X-gallons of water per fish" doesn't typically apply with mbuna's as it would with many other types of fish."

I have heard of the "strategy" of overstocking to cut aggression, but as far as putting to much "bio-load" on this tank, this tank far exceeds capacity. As long as these fish are eating & breathing, they are putting a strain on this tanks biological filtration. He could do a 50% partial on this tank every day, & it wouldn't be enough. Regardless of species, overstocked is overstocked.