Pekin duckling helllp

[Rosie1115]

I am also new to ducklings and have 8, 3 are Pekins and one does not seem to be right , he trips on his feet and does not walk as good as the others and today I found him stuck on his back twice already , the first time was in the morning and I’m not sure how long he had been like that since I had checked them last night. I have added poultry booster to their food and also just purchased this niacin, is this safe to put in there water ? I was told to only use 100mg per gallon of water .