|This sounds like the start of a bacterial infection. If you have access, you should consider either Tricide NEo dipping, PLUS medicated food, I am partial to MediKoi. It's better made without top dressing or super heating. Checking your water quality is a good first step because high nitrates are a common cause of chronic illness among Goldfish, crowding is another. One inch of fish per ten gallons is a good rule of thumb, more on tjat is at KoiSchool.com
No matter what you ultimately do
about this condition, please, FIRST,
check your water for Ammonia, Nitrite, and Nitrate. To learn more about
these several important water quality parameters, please see this link. Establish that the Ph is higher than 7.0 using any of the many great test kits available. To raise pH you could use Baking Soda for the "quick fix" and then follow it up with a buffer. Make sure, too, that you have seen KoiCrisis.com - You can click on the fish there to get specific information about treatments and options.
Want a shotgun remedy for use on parasites and bacteria once you've ruled out crowding, poor water, high nitrogen or low pH?
Here's a perfect shotgun remedy that won't hurt fish:
(1) Salt to 0.3 or 0.6%
(2) Warm the fish no faster than one degree per hour, up to the mid seventies, or if you want to combat Koi Herpes Virus, use the same "one degree per hour" heating from their ambient temperature up to 86oF
(3) MediKoi food is, in my estimation, by far the best made, best formulated medicated food. It will help control bacterial infections.
(4) Dimilin handily controls comparatively rare but large parasites like Anchor Worms and Fish Lice.
(5) Prazi or Prazi containing medications controlf Flukes on Koi and Goldfish best.
Using all of the above at the same time can be highly
successful against most parasitisms and infections. The space in which
this is done should be the largest possible (100+ gallons), with plenty
of hiding-cover, algae or live plants, and plenty of wter turnover for
aeration. This protocol could be hampered when applied to
salt-resistant Costia. A Formalin treatment on the way
into the quarantine where the above will be applied will break the
lifecycle of Costia and prevent it emerging in the quarantine tank.
Thank you for your consideration,
Dr. Erik Johnson
Here are some sites that might be of use to you:
: All of DrJohnson.net
Koi Health & Disease Research Laboratory - Koilab.com - Research facilities for Koivet.com's Dr. Erik Johnson.
News From Koi Pond & Water Garden Industry - Koinews.com - News from the Koi World, updated as it happens!
Classified Ads By Koi Keepers, For Koi Keepers - Koiclassifieds.com - Don't store that old pump. Sell it! Low listing costs!
Koi Clubs - Searchable Koi Club Locator
Koiclubs.com - This is your chance to find a local koi club, organized and searchable by state! It's free! Don't leave it to your president to list your club! List your club so people can find you!
Koi Health & Disease Information, Medications Treatments and More
KoiVet is the oldest, and best fish health site regarding Koi and Ponds. Message boards, FAQS, chat room, etc. Koivet.com - Dr. Johnson's mega health site, 24 hours a day.
Koi Health & Disease Information, Video and Book
According to Dave Hester: ""I have read the book cover to cover three times now and used up a highlight pen. Anyone that has bought one koi should have this book before they buy number two!"
Free Koi Club Web Site Designer - At KoiClub.com
Free websites for clubs. Sign up, FREE, design a web site using any of six FREE templates. Website appears as yourstate.koiclub.comValuable Treatment Resources:
Aeromonas - Koi Ulcer Treatment & Cure - Tricide Neo - Fight infections, easier than injections, safe and simple.
Koi & Goldfish Pond Medicines, Treatments and Information, Usage Guides - PondRx has almost every medication, resource or help you could need with your fish health problem, complete with usage guides written by Dr. Erik Johnson.
Fish Health Information Find a Fish Vet - FishDoc.net
Fishdoc combines the writing stylings of Frank Prince-Iles and Dr. Erik Johnson on Koi and Pond health! Best of all, you can find a fish vet near you!
Medicated Food For Koi & Goldfish Ulcer Disease - Now! Two kinds, available overnight.
Safe for Koi - Fluke (Trematode) Filter-safe Treatments - Prazi - Bulk praziquantel for Fluke Control. One treatment, no water changes, no filter effects.Koi Pond and Water Garden Supplies Resources
Discount Pond and Koi Supplies, Filtration, Koi Food and More!
Pondkeeping.com has what you need, when you need it.
Aquadyne Filtration, Koi & Goldfish Pond Bead Filtration / Filters
How about a filter that takes care of itself? Cleaning the filter in your Sunday clothes? That's how I do it! Fast and clean!
Koi and Goldfish Water Garden or Koi Pond Filtration, Food and Supplies
Steve and Janelle Raabe stand ready to help you, with a complete, and growing line of supplies for ponds! Phone support and the best stuff in the biz.
Flowerfish or Luohan Cichlid Fish Information - Buying, Showing, Keeping & Care
The flowerhorn is the most prestigious "big fish" in the tank. Each is a work of art. No two are identical. Colors get better every year!
Goldfish Information, Care and Supplies at GoldfishWorld.com
Articles, fish, pictures, and more await you at Goldfishworld.com - Don't buy a Goldfish anywhere else!