's do not "cure"
parasite problems. At best you end up with a reduction in the theront levels but it is quite rare if ever it would completely eliminate C. irritans
from the tank.
Your best course of action is remove all the fish
and treat in a <<quarantine tank>>
if you have a refractometer or failing that Cupramine
also in a QT
. As long as a fish remains in the system, the life cycle of the parasite will continue. As well, all future additions should go through the QT
process to eliminate adding problems to your display and keeps it parasite free.
A decent 20 gal
long and appropriate equipment + the refractometer would cost less than $100.00 and be a guaranteed long term investment.