That is great that you are seeing improvement. Bumblefoot can take a while to heal sometimes. My Pekin usually takes a few weeks to a month. So it can take a while.
I like to keep mine in a pen outside with my other ducks. And I put them in a dog crate in the coop. I find they do better when I can keep them outside. Playdates definitely cheer them up. I surprised you can fit 4 adult ducks in your bath

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Don't beat yourself up about it. You are doing great. Bumblefoot can be hard to tell in some ducks, especially since they are prey animals. You are taking care of the issue and trying to prevent it in the future.