You are so right!I think koi are more prone to disease because we keep them too clean … too much filtering and fussing to keep water perfect. Most fish would look better if kept in a big muddy pond
In my Dorado thread I talked about how I am trying to simulate "low tech" pond conditions in my aquarium because I too noticed that ponds with anaerobic tend to have bigger and better looking kois. The Japanese have all kinds of additives to put into the man made backyard ponds to get back some of the stuff taken out.