I hate to say it, sorry, but I am thinking flukes.
I did a quick lookup of Paraguard:
http://www.seachem.com/Products/prod...ParaGuard.html
... and unfortunately I don't see anything that lists specifically against flukes or flatworms. As far as I understand, flukes are a flatworm and thus require a specific medication against flatworms, such as praziquantel (which is available either as "praziquantel" or as "Prazipro" which is a liquid solution but contains praziquantel as the active ingredient).
http://www.uskoi.com/prazipro.htm
I'm trying to find a product description for the praziquantel powder that I used to treat skin/gill flukes when I had a fish with them but as it was a year ago now I'm having trouble finding the webpage I found back then. I'll keep searching and post it if/when I find it.