Perform a fifty percent waterchange, and clean the tank as well as reasonably possible without causing undue delay in treatment. Add all at once in the case of epidemic mortality. A word of caution on SALT though. It should be food-grade or non mineralized cattle feed grade, NON iodized salt. Brochis britskii cats, and native or wild caught Discus.
Rams dislike it also.
Submerged plants perish in the salt dose as listed above. Do not use it if you have live plants. Note the divided dosing, so as not to add it all at once. Introduction to the video. Get an AquaDyne.