I would use any medicine. you can lower the salinity in the qt tank to 1.009 and keep it there for 5 weeks and then slowly bring the salinity back up to 1.025 over a course of 2 weeks, and your fish should be free of ich. I wouldn't use anything in the tank. The ich that is left in the tank will die off without anything for it to host on. this treatment is called hypo. Due a search on hypo salinity treatments and you will get good driections on how to do it.