Hi,
I have 4 Pekins and they sometimes go through periods of not eating their pellets as much too. I think several things affect their appetite such as extremely hot weather, mating, molting, etc. I've sufficiently spoiled mine and they get a variety of veggies and fruit. I try to get them either leaf lettuce or romaine as both have better nutritional value than iceberg lettuce. They also love chopped cucumbers, watermelon, apples, and spinach. On a couple of occasions I have boiled eggs, let them cool and then chopped them up (shell and all) and given them to the ducks. They do eat them and the calcium from the shell as well as the hardness of the shell is good for them. Ducks do not have a gizzard like chickens, so they pick up and eat pebbles & stuff during the day to help them crush up what they eat. Try to avoid breads & the like. They will most likely eat it (although mine won't because they've not been given any) because it is not good for them. It makes them overweight and the nutrition is just not good. If you have access to Dumor brands of feed, they are pretty good. What I give is Dumor Poultry Feed Grower/Finisher. It is in pellet form and the ducks seem to like that best.
GrammaDuck