Congratulations on your new ducks!
@Adalida had some great suggestions - I'm a big fan of Vetericyn (used with amazing results) and elastic bandaging like Vetrap (so many uses!), too.
I keep some Sav-A-Chick on hand and also make this electrolyte recipe when needed:
http://www.communitychickens.com/homemade-electrolyte-recipe-hot-weather-and-acidosis/. It was so hot and humid here (central KY) this summer, I actually drank a lot of the electrolyte mix in flavored water kefir. It tastes pretty salty, so mixing in a beverage makes it more palatable for people, IMO.
I make probiotic beverages like kombucha tea and have quite a bit of kombucha vinegar on hand. I use it for many things and splash a bit in the chicken and ducks' water when it's not extremely hot out. It does cause accelerated algae growth in the ducks' pools in the summer, so I guess the algae like probiotics, too.