it's up to you. I'd personally go the fishy route only if the regular water changes for 2-3 weeks don't work out. Another option would be to use a commercial wormer that you add to the water. Those are geared at all kinds of worms, parasitic internal nematodes and tapeworms usually, but they'll definitely work on harmless planaria. They're all worms. Something like Jungle Internal Parasite Clear would be perfect, as it doesn't contain copper.