I would recommend salt for any sign of diseases that your discus gets. I would say that it is the miracle medicine for them..
I'm a breeder/hobbyist and I only use salt as my treatment for ill discus. Chuck aside all those potassium, formalin, Malachite and Methylene. These chemicals tends to push your sick fish to the limit..essentially killing them if proper dosage are not administered..
The following are some easy to use dosage:
For prolonged immersion (24hours) - Make a 25% water change before hand. Add 5 grams of salt per liter. Keep this treatment for 2 days. generally kills all the external parasites and bacteria especially flukes!!
For serious cases ( salt bath) - Take a small pail or tank. Add 15 grams of salt per liter. Put the sick discus. The tolerance of each discus varies. Generally ranges from 3 - 30 mins. Watch them carefully till they tilt over. U should also see interesting discoloration of the discus. When they tilt, remove and put back in normal freshwater. This treatment can be repeated as many times as neccessary..try to keep an hour between baths.
I can assure you that tis is my regular mode of treatment and it works for me.
Dont worry bout the salt level..they can take it