It is fine to use crumble/pellets. I often ferment feed for my broilers because they seem to do well on fermented feed and that's what I use and what a lot of other people use as well.said it was fine to use crumble/lay pellets.
That's a question best asked in the duck forum.have you found a higher protein content to not cause these issues?
Are you feeding them once a day? I usually put the fermented feed out twice day to make sure they get their fill before going to roost.
I think if you just cut out the corn/ scratch and feed fermented starter, grower, or all flock everything will be fine. It may cost a little more, but then you don't have to worry about whether they are getting what they need, they'll grow faster and be healthier. Best of luck!