mmm... I think most people will agree that adding medicines to your display tank gives us all the heebejeebies...

If the zoo's are the only thing acting unhappy, and you can, I would move them to another tank if you can (being concientious of acclimation) run carbon on the water in the other tank to clean any residual trace up...

The other option (the one I would probably take (being that I over react) would to be change a nice portion of the display tanks water, run a ton of carbon, and find another way to defeat the problem.

Personal opinion, regardless of whether it is a store you trust or not, research it before you use it. Don't take some kid at a fish stores word that it was ok in their reef, every reef is different.

hope that helps, and good luck.