As with many of the fish diseases. Pulling fish and treating them and allowing the system that they were in to go fallow will kill off any parasite in the display tank. I am unsure of the Lifecycle of Black Ich (turbellarians) and how long, but with everything else 76 days is the standard fallow period to allow dieoff.I need to treat my whole aquarium, the problem is in there, QT tank wont erradicate the parasite of my display tank