Also, I actually was able to find a niacin powder online that I could put in their water.  After one of my ducklings passed away suddenly from what looked like maybe aspiration, I stopped giving them the brewer’s yeast and switched to supplementing their water.  It’s probably just in my head and the yeast probably wasn’t the problem, but it was one of the changes I made, and I found it to be easier too.  Just do some research first if you decide to go this route to make sure you’re getting the right thing.  There are a lot of different “niacin” types, some suitable for ducks and some not.  Also you have to keep in mind that ducks don’t consume all of their drinking water, so dosage is again tricky.