Simply Koi and More Koi

I have a kajaku thats has been sulking now for about 2 weeks he feeds well with all the others then goes into a corner and sulks the perameters are good PH is 7.5 ammonia 0 nitrite/nitrate 0 temp 20d I have scraped him till I am blue in the face and nothing shows.any ideas dunc

try a strong salt bath see how it goes, other than that it sounds like you may have to do a gill biopsy

dunc

cheers dunc