Treating the condition is not really effective, you need to find the cause and eliminate it.
Unless the root cause is taken care of, it will always come back It is a chronic condition that manifests over time
Nitrate,due to too few water changes and maybe along with some other stress agent are the most common cause.
Reducing nitrate with water changes usually does wonders.
But it could be.... nitrate in combination with stray voltage, or other out of wack water parameters, badly chosen tank mates,, too much/too little feeding of the wrong type food,, all these and many others could all contribute to it.