NO, just put 1ml over treats they will eat right up. You do have chick grit don't you? If you are going to feed them anything other than duck food they need it for their digestion. Just get the little bag and put it in a little dish because once they start going outside and digging around in...
Since you're going to the farm store you should probably pick up some B-complex vitamins too. It's so good for them and will help with leg strength and about every other thing you can think of.
You might want to try feeding them scrambled eggs too. I know it saved @Miss Lydia ducklings that suffered from shipping stress which is possibly what's happening to yours.