I bought Storey's guide to raising ducks today and found out that I am apparently not feeding my ducklings right. I have them on 20% protein starter (non-medicated) but haven't given them grit or brewer's yeast. Can anyone tell me how much yeast to give per day and the best method (food, water, etc.) I bought 1 lb. of powdered brewer's yeast and I have 25 ducklings. Also, do I just sprinkle some grit on their food or what? Oh, I got my brewer's yeast for $9.98 from amazon.com, that was with shipping, is there a cheaper way to get it?