You didn't mention their water. Is it deep enough for them to get their head into (submerged)? They need to be able to get their whole head into the water in order to keep their eyes and nostrils clear.
I would change this water every day. Fresh water is important.
I would find a source for duck grower type chow. The protein and vitamins are formulated for waterfowl.
Ducks are very messy (as you have learned) I would increase their pen size and use some thick straw bedding (away from the water) to assure they have a dry place to sleep.
I would continue to read read read everything you can find on raising backyard ducks.
Good luck with your ducks. They are alot of fun. Enjoy

EVERY HOW MANY DAYS???????
there are too many pooping peeps in your little box and it is only going to get worse. I changed the straw THREE times a day. My pen wasin my garage but as they got older I made a day pen too. Now that they are grown they have a house a night pen and free roam during the day
I agree with READING EVERYTHING you can!!!!!
Put DUCKS in the search of this forum for old posts,there are many!!!!!
Ducks do get plenty of foot and leg probs and messy bedding can add to it. Are you building a larger pen?
I have two and a half acres plenty of ponds and creeks but when my flock reached 21 I realized it was too many to be clean and sold gave away etc til I only had 8 Everyone is happy and pen cleaning is so much easier!!!!!
Good luck from another poopy pet peep lover!
Tanya
My peep pen from 2 doors and chip BOARDs(grandson never caught any with the net HAHA!
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The DAY pen for peeps
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The adult night pen and house
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The ducks sharing the pond with a flock of IBIS!
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You must watch how much protien you give them too much youll have leg problems.

Ducks aren't supposed to get medicated chick feed. Switch them to something made for ducks.