Flukes are a constant battle in our pond.
I have found them alive on scrapes taken from the pond walls and shower. We use various treatments which basically just give them some relief for a while. I do multiple treatments 3 or 4 doses 5-7days apart.
Salt doesn’t bother flukes.
Pp only strips the mucous and doesn’t kill them.
CT good for stripping mucous and helps any raised scales caused by flashing.
Not sure about lernex and salt. I’d say follow the instructions.