There's several options to supply niacin to your ducks so you can do some research on here to learn more about other ways, but it seems the most popular way, and the easiest for me, was just to get a bottle of niacin capsules. They cannot be labeled "flush-free" or "time-release" - you just need plain old niacin. Some people have found them at their local grocery stores but I couldn't find the right type anywhere but my health-food store. I get the 100mg capsules. The ratio is 100-125mg per gallon of water. I pull the capsule apart and pour the powder into a gallon jug - I just re-used an old milk jug that I had washed out. I usually add some warm water to the jug first and shake up the powder as it dissolves better than in cold water. Then when it looks pretty dissolved, I will add the rest of the water. When it's gone, just make another batch! This is the water your ducklings should get for at least the first 10 weeks for drinking. I did it for 12 weeks and now just give them some niacin water here and there, especially in winter when I know they are not able to get a lot of bugs (good source of niacin) You can also sprinkle brewers yeast on their food if you don't want to mess with water. I liked doing the capsules with water because I knew I was getting the right amount. Hope that helps!!