My ducks’ favorite food is DuMor Duck Feed. You can get it for like $7.99 per 10 lbs bag at Tracor Supply. I like that it’s not too expensive, & I don’t need to haul those bloody 50 lb bags. If you need it to be even more cost effective, you can go with the Purina Flock Raiser for like $26.95/50 lb bag. My domestic flock of between 40-50 ducks will all eat that, but it isn’t preferred. Matsuri is probably far and away the highest quality from what I have heard, but mine only like to eat that when in the water. They are kind of “odd ducks” (haha - pun intended). Lol! Also, it’s twice as expensive as the Purina Flock raiser so I guess it also depends on your budget, how many ducks you are needing to feed, etc.
With regard to fruit and veggie scraps - no citrus either. I love that they consume all of our strawberry tops, salad scraps, etc. There is really little to no waste. Hope this info helps.