| Photos would help.
If it is fin rot, the first step needs to be to get at the source, which is usually poor water quality and decomposing debris in the pond. While that is being worked on, the fish can be treated in a properly filtered QT with any of several antibiotic medications available. I do not know your level within the hobby, so I'll assume you are a novice. Experienced folks will tell you that injection is best, but I realize it is generally not practical for beginning level hobbyists. Check for bulk-size commercial products available for the pond and aquarium trade. In much of the country, however, you are going to have a real challenge unless you can heat the water to around 72-75F.
Where fin rot sets in, there is usually a weakened condition that allows all sorts of parasites to take hold. These need to be checked out. Using a microscope is best.
Check the AKCA website for a koi club near you. See if they have a Koi Health Advisor who can come assist you. Also, check out koivet.com . That is one of the better sites for basic koi health issues.
Good luck. |