Your right mike, stress is also a factor when you get bloat, i forgot to say that.
But i think that food is not something to underestimate, especially with Mbuna's, in the wild they got also a lot of different things to eat.
If they will survive with one sort of pellet, sure they do.
But we like to take care for our fish the best way as possible, and i think that you will be not happy when you get every day the same food over and over again.
about floating food, cichlids in the wild also hunt on mosquito's above the water, and there quite able to push the air out of them through there gills, with frontosa's it's a other thing, they can hold air.
But i never saw or heard that with our malawi friends.
so, bloat is a combination of stress, food supply and water condition.