Anchor Worms

Lernea elegans, the most common type of Anchor worm affecting Koi, is a real threat. They attach ventrally, they hold on for about 14 days, and they reproduce copiously. The wounds they create almost always infect with Ulcer disease bacteria, Aeromonas, and then you have two problems.

Treatment can be undertaken with Diflubenzuron
                          
I do recommend removing any adults you see attached and swabbing the wounds with Iodine or mercurochrome but when you use Diflubenzuron, it's not necessary. I do also recommend also feeding an antibiotic food when you see Lernea to head off problems.

Fish Medicines
Learn about fish medicines, what they do, and where to get them.

PondCrisis.com
If you have a koi, pond or fish problem, this site takes you through twenty easy questions and at the end you know what you need to fix in your pond to create restored Koi health.

KoiCrisis.com
Koi Crisis has a symptoms chart by system you can choose the symptom by fish part, and resolve a lot of Koi pond fish problems or at least, learn about them understand how to remedy them.

Koi Food & Feeding
What should you feed your koi? How many times per day? Is Corn really that bad in a Koi diet? What are the most common feeding mistakes people make? What's the best food?