is it with a mama or are you brooding? I'd first try adding some un pasterized ACV to drinking water. make sure it can dunk it's head in so it can clean out it's eyes and nose but not climb into and accidentally drown. use 1-2 Tab to 1 gallon of warm water. If this doesn't help clear it up with in a few days or you notice it getting worse or other symptoms then you might want to get an antibiotic for treatment. When ducklings /duck eat they always need water deep enough to duck their heads into but ducklings can drown so it has to be a safe container. I have used a plastic container with lid and cut hole in lid just large enough for them to get their heads into but they can't climb into then you just make the hole larger or got to next size container and cut a larger hole. Please let us know how duckling is doing.