^^
Not for adult fish, even dwarf species.
Everyone knows the "inches per gallon" rule is just as flawed as "watts per gallon"... they're general guidelines that don't always apply properly to every situation. Now, I'm not about loading my tanks up to the max, but 25 6" mbuna in a 200 gallon seems rather on the empty side. I have 17 5"+ mbuna in my 75 and on average I can only see about 6 of them at any given time.