activated carbon adsorbs chemicals in the water, so you did right by getting it out before medicating because if not, it would be wasting money :)
Turn on the filter, it also helps keep the salinity in check because some salt mixes are of poor quality and may make your salinity level change a lot.
In my personal experience, i moved him to an isolation tank(better for me because i had live plants so i can't add medicine readily) and then i add salt and methylene blue to the water and do partial water changes everyday or every other day. Bottom line is I want her to have superior quality of water. It also helps to give her good food, it will reduce stress and speed up the process. I medicate for a full week, even if I see good signs already ,to prevent it from coming back up again full blast. It worked in my case, i hope it will help you :) Good luck!
Experts please correct me if i'm wrong! :))