Any food other than the ducklings starter feed they will need grit [chick grit is best when tiny.]
If it's safe to feed to chickens then it's okay for ducklings you just want to make sure to not over do since their feed is where they will be getting most of their nutrients.
If it's safe to feed to chickens then it's okay for ducklings you just want to make sure to not over do since their feed is where they will be getting most of their nutrients.