I am hoping someone can help. When feeding the fish today I noticed that one of the kois was eating strangely, then when it turned I saw that on one side of its face was deformed (I hadn't noticed this before today). I researched the symptoms it was showing and it looks a lot like mouth rot. \nI am currently doing a water change in the pond, so can't measure the water levels, but I will describe the pond. It is 16x12x4 feet (4784 gallons), using a PondXpert SpinClean 20000 filter, as well as having a waterfall running from a small pond filled with watercress. The main pond itself has lots of oxygenating plants, there are around 8 koi, 10 gold fish, 3 or 4 rudd, a shoal of minnows, and a few stickleback. \nI haven't been able to catch the ill koi yet, but want to know if mouth rot is contagious? What is the best method to rid the pond of parasites? Any advice/help would be greatly appreciated, thank you in advance.