Just from my personal experience- maybe it can help:
I had 4 ducks in a 6x10 enclosure and was feeding them crumble from
Tractor Supply and had 1 water bucket that I changed twice daily and their kiddie pool
During that time I battled weight loss, bumblefoot, egg problems etc.
I have expanded their pen and now it's almost 20x50ft (thanks to craigslist)
I switched to Mazuri waterfowl maintenance and mix a little of the
TSC feed just to make it last because it's more expensive.
I leave out a bowl of oyster shell constantly.
They have 2 pools and 5 water buckets (which I now have to change a few at least 3 times a day because it's freezing)
I clean out their house completely about once every 2 weeks and top it off every other day.
At night I feed them dinner about an hour before I lock them in their house just so they have time to wash it all down. Once they're locked up they get no food or water because it's so cold.
It's a lot, and it's exhausting, but they're healthier and happier.