Was it definitely the same one? Waterlife do several different parasite meds, I know because I ended up making two separate journeys to the not-so-localFS after I got the wrong one first time round!
I emailed them to ask about which to use (because I was a bit worried about the snail situation) and this was their reply:
Sterazin is perfectly safe with mollusc, it is not safe with
shrimp, crayfish or crabs. Octozin is safe to use in aquaria containing
all invertebrate species and is the medication of choice if the fish
have an internal protozoa infection.
Regards,
WATERLIFE
They also have Paragon and something else I think. I would have no idea how to tell the difference between an internal protozoa infection and worms (other than doing an autopsy?) but I had a hunch it was something that had spread from one fish to another and guessed it was worms, hence starting on the Sterazin.
But... I guess there are lots of different types of parasitic worms, right? So this might be effective on one sort but not the other. And I suspect it would only have to work in a majority of cases for them to manufacture and sell it, that's business, right?
Re flubenol, when I was researching what meds to buy, I got very confused with the whole flubenol situation, there seems to be various different standpoints on its legality, you can still see it on ebay sometimes (not that I would advocate breaking the law) so not sure how illegal it really is.
I'd try that discus stuff before I tried pig dewormer though. I just think that unless you are a vet and/or you really know what you are doing, using meds meant for mammals on fish = dodgy plan.