to be honest im not sure, looking around the site there is a lot of disagreement about what type of salt should be used, (iodised, low sodium, sea salt, kosher salt, aqaurium salt) and how much, some people saying 2 litres 2 teaspoons in effect one teaspoon per litre.
but on the health page it says
Holtfreter's solution in higher than normal concentrations is also effective against Columnaris, as is the use of a salt bath. Place the animal in a salt bath for about 10 minutes once or twice a day. A salt bath is prepared using 2-3 teaspoons of salt (table salt, cooking salt, or iodized salt, but not "low" or "low-sodium" salt) per litre/two pints. Don't leave the Axolotl in the salt bath for more than 15 minutes each time, because the salt will start to damage the Axolotl's skin and particularly its gills. Of course, this is all useless if the animal is still under stress when put back in its aquarium (strong-flowing water, high water temperature, bad water quality, etc....).
and thats what i have been doing. using 2 teaspoons per litre and im not sure if it has been effective because after 3 days of baths, there are still large clumps under bananamans gills and i am begining to get worried