About the mild stages of Podermatisis (bumblefoot), I'd first correct the underlying cause of the issue so it doesn't repeat itself, first thing I notice is how small your brooder is, I'm guessing you have to clean it A LOT, you probably can't keep up with the mess, and the majority of the time the ducklings are sitting in waste, correct me if I'm wrong. I would start soaking the leg in Epsom saltwater for a few days to loosen up the flaking a bit, and then start applying an antibacterial ointment to the area twice a day until it disappears.