How old are they? My understanding is that mash is not great for ducks because it gets stuck under their tongue - pellets are better - but that's the theory. If yours are coping OK, then it should be fine (and given the state of their food once they've mixed it all up with water anyway, it's pretty much duck-made mash).
Then it's the growers/layers debate. It's all about protein/calcium etc. but it's hard if you've got them all in together. I've got chicks (not tiny ones but a few weeks old), adult chickens, a duckling (nearly three months old), adult ducks and geese in together. In theory some should be having layers, some waterfowl growers (my goose breeders put them back onto growers/finishers when they'd finished laying) and some chick crumb/growers. At the moment I'm putting layers into the hen feeder which is harder for the ducks and geese to get their bills into, growers (mixture) into an open bowl and a few chick crumbs into a small bowl in a run within the run that only the chicks seem to go into (never seen any waterfowl in there). Then I just have to hope they find their own balance - the chicks prefer the smaller pellets and crumbs anyway so that works, the ducks prefer the open bowl although that means the laying ducks might not be getting enough calcium and the hens just pick at everything.They all have lots of space for free ranging so I hope they balance their own nutritional requirements to some extent - just as nature intended.
H