There is definitely survivors deep in the rock work, you cant see them all. The treatment will not hurt, but the toxins will. If you killed most then in @ 3 days after running carbon and doing water changes hit the tank again. If you dont kill them all you will battle this again. The medicine does nothing to the tank, but the toxins from the worms will kill.

When I treated, I didnt think I had aproblem because I did it early. I followed all the directions and still had flat worms. I dosed agin a week later and then again 3 days later and have not seen any since.

Use carbon afterwards to get the dead worm toxins out not the medicine.

Hopefully that makes sense.