Hmmm we used to have goldfish with our koi, but my parents messed up and didn't listen to me when I warned her about getting new rocks for the bottom of their pond. After half our fish were dead she finally got them all out of the water and finally decided to check them under vinegar. What do you know, they fizzed like crazy.
I was not happy!!
Right now we only have koi and one of the really fat goldfish with koi markings. I don't know what they are called, it was our neighbors fish, but when we had a flood warning she decided to get rid of it and tossed it in our pond. Random new fish, glad he didn't die of shock! It's fat and has long flowing tails. Adorable to watch him swim. :)