I purchase a Jap tancho goshiki about 6 weeks ago, Lovely grey body and bright red tancho marking. Over the weeks the body colour has remained much the same but now the red tancho marking has gone a dull red and black spots are now appearing within the red.
This was purchased from a reliable koi dealer.
My water is okay for Amon, Nit,PH and Nitrate, I feed orchard prem and colour.
Previously kept isralie koi and never had this problem.