Question
Hi.It is march water temp is around 45 consistently(i have water heater) just noticed on one of my bigger koi fuzzy white spot on its head.I added salt to 2% around 2 weeks ago but don't see much improvement.I am afraid to medicate entire pond yet have no means of getting the sick fish out-pond is 4ft deep.Need your advice .Thanks

Answer
If it's fuzzy, it may be fungus.  That may have developed if the koi got a cut on his head.  The fungus then would take advantage of that.  Normally, the dosage of pond salt is 0.1% to 0.2% (if you don't have plants).  If you truly have 2% salt in there, and the fish are tolerating that much, then the salt should kill off the fungus.  If not, fungal medications may work.  They are expensive so it's best used in quarantine.  How do you normally work in the pond since it's 4 feet deep?  Swim?  It is a might bit cold for that!  I was in my pond today at 41 degrees F but in hip waders since it's only 26" deep.  You might also try all natural PimaFix by Aquarium Pharmaceuticals which kills fungus.  It may be expensive for the entire pond but should be relatively safe.  Just be sure the pond is well aerated as it can lower the oxygen levels.

Good luck!