copepods (anchor worms), amphipods, isopods, etc. Any parasite with an exoskeleton. Sharks are typically loaded with these so I started using it over Dylox. I had a nasty battle with a type of amphipod that was burying into the skin of my sharks until I found it. It is harmless to fish, so I started using it in my QT protocol. It is a chitin inhibitor and therefore does not kill until they need to molt. Also prevents development.