Often the best treatment is fresh dechlorinated water from water changes and good nutrition, however, it is also important to find to cause.....
Can you post a pic, do the fin edges look irregular, crusty and discolored
What size tank, type of filter, live plants, type of substrate and decoration, water temp, additives used, appetite, type/amount food/feeding, any tank mates, how long have you had him, any other health issues and types of treatments tried, how much and how long on the salt treatment...