I just looked at the nutritional yeast that i have and it does list iron I'd say it must be in smaller quantities than the poly vi sol. On my container it lists niacin at 370% and iron at 4% so very small amount. go with the niacin tabs you just have to crush and mix in their water 125 mgs to 1 gal of water and you may have to mix it a few times a day to keep it from going to the bottom Brewers yeast is 1 Tab to 1 cup of feed.
How are they doing today if still improving maybe not give the poly and start the niacin and just watch there isn't a relapse. Read the post Amiga gave you probably some idea as to how long to give the poly vi sol. I was hoping @Lacrystol would give us her ideas since she hatches regular. Not sure if @casportpony uses poly lets see if she'll say. I really like Nutra drench because it is formulated for poultry and i have used it many times and know it is safe. it can be given straight into bill also. Goes straight into the blood stream. by passes the gut. Pics when you can.
Just joined in, Sorry, I'm so late, what's the results so far??? Polyvisol doesn't have FAST results with Ducks, it takes longer for it to actually take affect.. It's GREAT for chickens but not so much with ducks, it will do the job but you have to have more time and patiences.