There are a couple causes of popeye, includining TB, and injury but if it effects more thaan 1 fish, and if it effects both eyes it is almost always a gram-necative bacterial infection. The clean water and salt, along with melafix if you so desire, don't hurt most fish, and are good recomendations for almost every tank at all times. For acute cases of popeye in a single fish it is best to use a hospital tank, for several fish at a time treat the whole tank, clean it, do a partial watyer change (30-50%), and treat with a broad spectrum antibiotic. Maracyn Plus, Binox, Tri-Sulfa are all known to work.
It is true that a good, clear description of symptoms, current water parameters, a mention if it is just one fish or more effected, and pics if possible, all help ensure a correct response.