Koi - Pond - yes salt 

Salt in the pond Yes, I always put some salt in the pond in the spring one reason is mucus the fish produce mucus on the body which helps stop fluke and any other parasites on the koi’s body.
It also helps the Koi with healing.
Any new Koi I will always put into a Salt bath before putting them in the pond.
DO NOT USE SALT IF YOU HAVE PUT FORMALIN IN THE POND AS THIS CAN KILL YOUR KOI.