Bleach is pretty harsh and will kill erven good bacteria so I wouldn't use it. @Amiga was talking about vinegar/salt solution working to clean our coops maybe something like that or Poultry dust worked into the ground real well. Once the worms are expelled they will be dead but you'll need to reworm again in 10 days to kill any eggs that hatch inside your ducks. Depending on what you used to worm with.
I think I'd just go woth the Vinegar and salt if your pen is hard packed. lets see if we can get @Amiga for help on the vinegar and salt. Or maybe others will have a solution that is natural I honestly don't think you have much to worry about in your pen if they are only in it at night and free range during the day. You might could just wash it down good with the hose or just water and vinegar.
