salt will do nothing in prevention
like the above poster water changes are the best prevention
try and keep nitrates down + a high quality food
i used salt back in the day when it was all hyped up, i found its pointless to use salt in a freshwater aquarium, its not proven to have any benefits at all.
if you need salt to try and fix something (disease, nitrates etc) then you better look into whats causing the problem and fix it with water changes.
unless you keep african cichlids (rift lake salts) theres no use of salt in a fresh water set up