Based on my own theory that ducks need more quality saturated animal fat in their diet. I thought about it, and to me wild ducks eat mostly grub (saturated fat & protein) they find in the mud and then supplement with roots and vegetation. Three things made me think my own ducks needed more fat:
#1, I began exploring this more when I fed my ducks a bunch of chicken roast drippings one day (mostly fat, some broth..) and then the very next day I had calm, content ducks (not dumpy). Their usual noise and slight obnoxiousness came back within the next few days.
#2, I had a lone wild female mallard join my flock... She never left but over time I noticed that her beautiful glossy feathers and feet went kind of dull. Not bad or unhealthy looking, just far less amazing than when she first came.
#3, Since moving to my new home where they can range my backyard which is a 30x larger area than they had access to before, they have all beautified. They molted from the stress of the move but they all look sooo good now. (except my one KC that has never molted her wing feathers!!) The feathers that came in were a lot more sheik and soft than they had ever been. They had access to some dirt and vegetation before but I'm sure it was picked clean of grubs.
Also my belief that an overcrowded pond is a noisy one not because of # of ducks but because of the nutrient deficiencies they are suffering from over picked resources (bugs, fish, vegetation).
I would raise mealworms but I just can't commit to that yet. Fodder is enough to keep up with. So I chose pig lard because I have an excellent source, I get it from the farmer. The pigs roam large outdoor grassy areas in the sunshine and are fed extremely quality ingredients. I mentioned "pastured" before just so people didn't think I was recommending going to the grocery store and buying that crappy hydrogenated lard from CAFO pigs.
Right now I drizzle about 1-2 tablespoons a day on their fodder grass for 6 ducks. I do believe they are getting a lot more fat than before but still not enough.
Like I said, this is my theory and so its something I'm slowly experimenting with