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I would think yes. But you would have to re-dose the percentage of the meds that have been removed by the PWC. Eg: 30% PWC, you would have to add a 0.3 of the dose.
Or you could remove all the meds and treat with just heat and salt. http://www.aquahobby.com/articles/e_ich2.php
Ideally you should have done a PWC before you started treating.
Keep a close eye out for a comeback. I personally am not a fan if kick ich. What happens on the parasite is that it looks like it`s gone when in reality the parasites have fallen off and at the substrate over 200 little ones called tomites will come from each one. Then the parasite comes back with a vengence. Read these articles on info about the parasite and treatment methods.