skin problem on Koi fish

Question
the tank has bee set up for 2yrs, its a 30 gal., 3-Koi fish & 2-pleco, filter is a whisper, unk. on pH levels, water change approx. 2wks, replace approx. 10gal.

1 of the Koi fish had some redness around the mouth, now it appears that the skin around the mouth and nose is coming off. It appears that the skin is being eaten away by some kind of bacteria? You can actually see the cartilage where the skin is missing.

All the other fish are fine and do not appear in any distress.

Answer
Hi Tony;

It sounds like mouth rot. It's a bacterial infection and is related to water quality. Make a 25% water change right away and do them daily for the next 3 or 4 more days. Vacuum the gravel at the same time. He may need an antibiotic as well. You can find them at your local fish store. I would use something with tetracycline in it.

All tanks really need a weekly 25% water change with gravel vacuuming. Yours actually needs it twice a week though. Your koi are just "too much fish" for a 30 gallon. They need to be in a pond or a tank of at least 500 gallons. All koi fish grow to be over 3 feet long and are very messy guys. Their waste is building up in there and it's only going to get worse for them as time goes by. You may have heard that "fish only grow to the size of their aquarium", but it is a myth to a certain extent. If your fish actually stop growing because the tank is too small, they are in danger. They usually die of old age far before their time, get sick like one is now, or their organs fail. Some fish actually continue to grow anyway and develop crooked spines and other deformities in order to continue to move in the tank. That's very sad. So, find a pond where they would be happier or invest in a very large tank. They will love you for it!

I hope he feels better soon...

At Your Service;
Chris Robbins