Oh wow that's a lot of money for Brewers yeast. Have you priced nutritional yeast? It is almost the same. I find it in the bulk foods section at my grocery store for $10/lb. have you checked any nutrition stores to see if they carry it?I started with 1 tbsp per cup of feed and then dropped it down to 6 tbsp per 8 cups of feed. If I ever raise ducklings again I found a place on the internet where I can get the brewer's yeast for something like $8 per container (I'm paying $15-$19 retail) but the shipping is around $14 or $15 so I could estimate how much I needed and buy in bulk. Don't think I'd put anything in their water since they seem to spill and waste more than they actually drink. Live and learn.