I just posted in your other thread too, but wanted to chime in here. Niacin deficiency is a very common cause of shaky legs, and easy to treat. You don't need special 'duck' niacin--human capsules will work fine. And putting it in the water does work fine--it's worked for me and it's suggested by Dave Holderread, the leading waterfowl expert in the US (and among the top in the world). But the other methods (as outlined in your other thread) work just fine too (and are also suggested by Holderread). Just be sure to keep the dosage within approximately 150 mg per gallon (give or take 50 mg either way).
Use whichever method is easiest for you. If niacin is the culprit, you will begin to see results in one to two days.
A fourth option is to buy feed that is formulated for waterfowl, but they are hard to find. Mazuri makes a good one, and Purina makes a feed called Purina Flock Raiser that is supposedly very good (but it's NOT the same as their standard Purina chick feed, so be careful to get the right one).
I would be cautious about putting the niacin powder directly on the food, as it would be difficult to get the dosage right, but others have had success that way so it may work for you.
Of course, there are other things that can cause shaky legs. If you have an avian vet, you might want to have them chime in as well. If you treat the niacin deficiency and are not seeing improvement in one to two days, then you'll need to investigate other possibilities.
Good luck to your little one! Hope you're able to find a niacin solution that works well for you.
