When adding medicine to treat fin rot, remove the filter cartridge or media. I have used Fritz Coppersafe for my fish and it worked great. The treatment lasts for 30 days “per serving” I also turned the temp up to 80 while treating. This type you can leave your filter/media in unlike others. When treating fin rot or ick one should treat the entire tank vs removing them because the new environment or settings cause add more stress on the fish. Drastic temp changes during water changes can also add stress and also cause other health issues. So treat the water with conditioner, stress coat/ammonia,nitrate/nitrite remover and live bacteria (if it’s a new tank). Just something that I have done in the past and continue to follow. Best of luck.