I'm glad you asked the question about feed, as I have questions too about whether I am using the proper food for my ducks. I live in central New Jersey in a rural town that has lots of horse farms and people that keep assorted poultry and other farm animals. I will share what I've been doing, but probably have more questions than answers unfortunately.
I thought it was interesting that Mo says they use chicken food in the UK for their ducks. I wonder if that is different or less expensive than what I've been using.
I'm pretty new to ducks too, having adopted three that showed up in my yard at the end of last summer (two most likely were dumped on the lake across from my house and found their way into my yard, and the third was a duckling that was abandoned in my yard by one of the feral farm ducks that live on the lake).
When I had asked at the feed store for duck food, they gave me "Gamebird Pellets" and that is what I've been feeding my three until I changed to "Layer's Pellets" when the two girls began laying eggs about a month ago. (The bag says "Gamebird Pellets" also, but apparently has different levels of nutrients).
I feed the lake ducks and wild mallards that visit my yard "Cracked Corn" in the summer and "Scratch Feed" (a mix of wheat and corn) in the winter, because it is less expensive than the pellet food since they are getting their main meals in the wild and are just coming to my house for 'snacks'.
Does this sound right to you experienced duck owners out there.....? Any suggestions or comments would be most helpful.