7 week old duck sitting on knees

[Keely Noodle]

So I hatched three ducklings in August and two are very healthy. However, the third was weak when born and I wasn't sure if she'd make it but she did and she's been growing up nicely but slower than the others. Recently though, I noticed that she doesn't have great balance and her tail is almost always tucked between her legs and she often likes to sit on her knees. Is this anything to be worried about?
I feed them growers pellets and a bit of grit and some treats like mealworms, lettuce and cucumber.

 

[sourland]

Do an on site search on 'Niacin deficiency'. These may be an easily remedied problem.

 

[chickens really]

I have had Ducklings that sit like that...Had nothing to do with deficiency in diet....Might be though in your case?....I feed Duckling starter till 8 weeks then Duckling grower till 4 months and then Duck finisher....
If it's fine other wise and runs around it should be okay...Try adding niacin, it won't hurt them....

 

[Miss Lydia]

Some of my Runner sat like that when young. But to be on the safe side I would supplement their diet with some extra niacin in the form of Brewers yeast or Nutritional yeast 1 Tab sprinkled over each cup of feed you give them. They need extra niacin till at least 10 weeks of age.