Hello Sammy, I just read that Wrinkle died and I read back through all your posts. Are you feeding your ducks the same food you are feeding you chicks?
Ducks need more niacin the chickens -- and pekin ducks need the most niacin of all. I am thinking that Wrinkle was niacin deficient. I strongly advise you to add niacin to the diet of your ducks to prevent future problems.
I don't know where you live but if you can get nutritional yeast (from the supermarket or healthfood store) you might add that to the duck's food. Or alternatively you can use brewer's yeast. Nutritional yeast contains a higher concentration of niacin but brewer's yeast is much cheaper. You should sprinkle 1 tablespoon(15ml) yeast over 1 cup (250ml) of duck food.
We give all our ducklings brewer's yeast until they are fully grown, and continue to give it to our adult laying females.
I hope you hsve no further problems with your ducks