I bought this Koi at Pet smart 2 weeks ago. I noticed a small black dot when I purchased it and they told me it was part of its markings. I put it in 40gallon quarantine tank with the 3 shubunkin gold fish I got when i bought it. I thought it was part of the markings on the fish but figured best to keep an eye on it. 5 days later it was very noticable and red around it. I went back to the store with this picture and the told me to use Jungle brand Fungus Clear fizz tabs. I bought it and immediately added it to tank. 4days later i changed 25% of water and added directed amount again. It is not getting better but dont seam to be getting better either. Sunny (my granddaughter named it) is eating fine and swimming around but now the top fin is down against body. Does anyone have any ideas of what to do? I really like this fish and am concerned its suffering. I'm not new to having Koi but DON'T know much about the care as when we bought our house the pond was established for over 6 years and the fish came with the house purchase. Ive had the house 3 years and have never had a problem or had a sick one none have died and there 8. They have had babies and ive given them to friends with ponds and traded with others. This is the first time ive had an issue and im at a loss of what to do next or how to help it or even how it got it! PLEASE HELP ANY IDEAS ARE BETTER THAN NOTHING!!!