Panacur is fenbendazole, different from flubendazole (trade name Flubenol)
mentioned in German fish books.
Fenbendazole is primarily effective against nematodes, and is only
moderately effective against trematodes (NOT monogeneans). To treat
trematodes in other animals, daily doses for 6-10 days are required.
I have used fenbendazole in feed with no adverse effects, but everyone I
know who has used it in water reported that fish died rapidly.
A much better and more effective treatment against monogeneans is
praziquantel (Droncit). Safe both in water and feed, it is my drug of
choice for monogeneans.
If she is seeing _Lernaea_, which is more likely (though there are some
monogeneans that grossly visible), Dimilin would be the drug of choice.
Denise