Duck food:
birth to 2 weeks 18-20% protein
Weeks 2-7 16% protein
Weeks 7-20 15-16% protein
.30- ,40 pound per bird per day
Butcher when fully feathered, Between 6 1/2 - 10 weeks there will be a 5-10 day window
If missed, wait another 6-10 weeks
My ducks are eating a turkey pellet which is 20% protein, plus whatever grass, bugs, kitchen scraps they can find. Also a very small amount of dry cat kibble daily for animal protein. Oyster shell free choice for the adults.