If I were you I would return it and purchase a "duck" specific feed. The bag in the photo is more or less chicken feed, which is fine but you will need to take an extra step to get the niacin level right. Here is the product line you need below from the Purina website.
I have had trouble finding duck feed sometimes, so I would echo Kevin565 - use this and add niacin (plain, not no-flush or timed release) - one way to do that is with plain niacin capsules in water (100 mg per gallon), or you can try brewer's yeast (a tablespoon per cup of feed), or B-complex vitamins in the water (using 100 mg niacin per gallon of water as a guide).
Those are the general guidelines I have seen on the Duck Forum.