Not that anyone asked, but I have been keeping koi/carp for years and never had a problem. I have been breeding fancy goldfish too, again without any of the above stated problems. The two worst things I have had, was anchor worm, and I had a 2 ft koi jump out and I didn't find out about it until it was too late. But Koi are known jumpers. Strange for you to have so many problems. Probably something they picked up prior to getting to you. This is one of the major reasons you NEVER put the water you get fish in, into your system. AND you are ALWAYS supposed to quarantine any livestock. Just like on a farm you NEVER turn a cow out to the herd without isolating first. It's the same here, you just have a smaller ranch. The anchor worm was my own fault, I put the water they came in, in with them. They had no visible parasites, but the cysts were in the water, and once given access to hosts and proper conditions came to life. You break your own rules, and it bites you.