Home - Koi Medication - Koi Parasites - Sick Koi Symptoms - Pond Water Quality
Site Links

Symptoms Finder

You'll get a picture of the koi/goldfish, you click on the koi fish where it's sick, or choose from several other behavioral options that your koi may be exhibiting.

What KoiCrisis Is For?

Outbound Links

Need Help Now?

We offer FREE personal help with your sick fish and/or pond water quality problem. Fill out our easy “Help Form” by Aqua Meds

Feeding Koi

What to feed?
What not to feed?
How much to feed?
What to look for in labels?

Aqua Meds®

Have questions about care of sick fish and/or pond water quality problems and how to treat them? We have the answers.

Fish Medicines

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


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.



Koi Diseases or Disorders of the Body

Koi Body sores or ulcers 
Ulcer Disease is almost always caused by Aeromonas bacteria or more rarely Pseudomonas bacteria. Clinically, I wouldn't know which because I rarely culture the pathogen. Why not? Because the results could take a week to return, and by that time, all the affected specimens would be dead. I have treated ulcer disease with the following drugs: Enrofloxacin, Chloramphenicol, Gentamicin, Amikacin, Tetracycline, Nuflor and Azactam. I inject these drugs.

Update: Ulcer Aid Rx™ has really changed everything as it replaces injections for those whom are afraid to give them.

No discussion of this problem would be complete without reference to swabbing techniques, antibiotic enriched feeds, injection technique, and prognosis.

Suffice it to say, that to save these fish, my core recommendations would be to get the fish into a heated environment, provide impeccable water quality by, swab the wounds with hydrogen peroxide or Mercurachrome, Feed MediKoi feed, inject Enrofloxacin and or Chloramphenicol, and hope that the next spring that the fish does not bloat due to retention of latent bacteria in the kidney after clinical cure.

Back to top

Koi Body features patches of raised scales
This fish is generally on it's way to Ulcer Disease

Those areas of raised scales will often "blow out" to reveal full blown ulcers. Sometimes, parasites have chewed those holes, and also very often, the owner will have rocks around the edge of the pond, at the water line. The fish, in their eagerness to eat will bash their heads and napes on the rocks and develop these lesions.

Here's what you do:


Update: Because of the over use or salt, there are now many “salt resistant” parasites. The NEW recommended treatment would be TERMINATE which is made to treat “salt resistant” parasites including costia.  

Back to top

Koi Body has red blotches on it
Again, I'd be on the lookout for a full blown Ulcer Disease case. I'd endeavor to test my water for all parameters pertaining to nitrogen and pH. We don't generally "dress" reed blotches with any medication, In these cases I recommend water testing, a major water change with Dechlorinator, then feeding medicated koi food while applying salt.

Back to top

Koi Anchor Worms protruding under koi scales
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 Malathion, Fenthion, Trichlorfon, Dylox, IDI Express and SALT. Salt works very slowly by killing the freeswimming reproductive forms. Malathion just kills the Lernea dead, but is dangerous to the fish. Fenthion is slow but safer.

Dimilin is great if you can get it. EPA and FDA will trounce you for having and using the agricultural version.

Caring for the fish: I do recommend removing any adults you see attached and swabbing the wounds with Iodine, hydro peroxide or mercurachrome.

I do recommend also feeding an antibiotic koi food when you see Lernea to head off bacterial problems.

Back to top

Koi Fish Lice Round "bugs" on koi skin are greenish and active

Argulus is a crustacean or branchiurian parasite most commonly encountered in ponds, but they are also found in aquaria. They are easily detected when they strike. They are greenish disc shaped organisms with suckers and small legs. They even have a pair of eye spots on the anterior end. They spend their time darting around in the water away from, and also directly on the fish. They lay their eggs in tubular structures on the glass and ornaments.

They can be very destructive to fish stocks.

They carry Aeromonas and other bacteria on their feeding stilletto and thus infect each fish they bite.

Treatment is by the application of the insect growth regulator, IDI Express, or Diflubenzuron.

Another method is more dangerous: Organophosphates like Trichlorfon, Masoten, Dylox, Dipterex, FLAW, Malathion and Fenthion. Anchors Away is also an organophosphate. i resist the use of these, because losses may result. IDI Express is superior to these compounds when fighting Argulus.

Back to top

Koi Tiny white pinheads in skin

Ich (white spot disease) rapidly kills smaller tropicals and goldfish, while sometimes sparing the larger varieties (fish such as Oscars and Koi). Damage to the gills is the primary way it kills, but damage to the skin with secondary bacterial infection may also figure prominently.

Its life cycle is roughly 2-5 days, but can be longer (5+ weeks!) if the water is cool, much shorter if the water is warmer. There is the old rumor that warm water eradicates it. This is substantially true when temperatures exceed 85 degrees, however; there are strains coming out of Florida and detailed by researchers at University of Florida that can survive and thrive up to NINETY degrees or more! Recall that many of our bread and butter species of tropicals come from Florida, and so may harbor this heat tolerant strain.

The parasite has a phase that encysts in the epidermis of the fish as previously stated (called a theront). It matures under the skin and finally drops off, falling to the bottom (becoming a trophont) to divide into numerous (hundreds) of tiny swarmers (tomites) that actively seek out a host on which to encyst and renew the cycle of infection. Because an important phase of its life cycle occurs on the bottom of the aquarium, it is for this reason that you can help limit infections with water changes made by siphoning the gravel, removing those dividing Ich packets.

Interestingly, some research at Oklahoma has revealed a strain of Ich that does not have to leave the fish and whose Ich packet (trophozoite) remains under the epidermis (safe from medications) and the tomites swarm out under the epidermis. The lesions look much like Carp Pox lesions, being large, flattened, and waxy looking. This parasite is harder to clear because it is the free swimming tomite that we can kill with medicaments.

1. Remove valued live plants.

2. Raise temperature to 80 degrees, tops.

3. Increase aeration!

4. Add one teaspoon of salt per gallon.

5. Twelve hours later, add another one teaspoon of salt per gallon.

6. Twelve hours later, add another one teaspoon of salt per gallon.

7. Within 48-60 hours of the second salt dose at 80 degrees, the Ich will be gone.

8. Leave salt in the water for another 3-5 days unless you're worried about your live plants.

9. Remove salt via partial waterchanges. (30-40% at a time if desired).

Update: Because of the over use or salt, there are now many “salt resistant” parasites. The NEW recommended treatment would be TERMINATE which is made to treat “salt resistant” parasites including costia.

Back to top

Koi Carp Pox White waxy globules in fins and skin
CARP POX is another virus of a dermatological nature, that also has a low transmissibility from fish to fish, and is again, not fatal, merely disfiguring. The lesions are soft and waxy, not warty and rough. The lesions should not be scraped. They may be differentiated from Lymphocystis because they do NOT cause the cells to become huge (megaloblastic) in size. The way Lymph does. There is no treatment, and lesions do not resolve as well as Lympho lesions do. You should be aware that CARPPOX lesions are very, very rare in North America. Many people report that warming the fish up, and salting to 0.3% are sometimes sufficient to remedy these lesions. The belief is that the warmth stimulates the immune response and the lesions clear on their own.

Back to top

Koi White patches (slime) on skin
Often, something is eating at the skin, such as a parasite like Costia. This is the most common slime-causing parasite. Still, many other parasites can ALSO cause the fish to appear slimy.

Just as often as parasites, slimy skin can be caused by a pH which is too low.(pH crash) The fish usually hang listlessly at the surface and develop strings of slime on them. A quick check of the pH will illustrate the point.

A soaring nitrate number as well as difficulties with other nitrogen numbers can cause the slime coat to become thick and plainly white. But usually this is not patches of slime. the fish are entirely slimy.

So, if I had a fish with patches of white slime, I would check my water for Ammonia, Nitrite, Nitrate and pH as well as carbonate alkalinity. Then I would salt the pond ot vat to 0.3% and if at all possible, get someone to do a scope biopsy on the fish. It is also possible to effect a remedy of the affected fish by swabbing the white slimy patches with regular drugstore strength hydrogen peroxide, one time. This is effective on the fish but not on the parasites or water quality issues facing the group.

Update: Because of the over use or salt, there are now many “salt resistant” parasites. The NEW recommended treatment would be TERMINATE which is made to treat “salt resistant” parasites including costia.

Back to top

Koi Scales coming off
The fish are flashing for some reason, or they are suffering from some sort of pathogenic attack. I have seen scales knocked out by Herons, cats, or kids with sticks. Fish will also knock out their own scales by "flashing".

Flashing can be caused by several things, including temperature changes, parasites, water quality changes, high pH or low pH, nitrogen accumulation, or bacterial infections.

The most common cause of flashing is a pH which is not to their liking, or a parasite problem. Among the parasites, the most common causes of flashing are Flukes and Trichodina.

Stabilizing the pH is a good idea to relieve flashing behaviors caused by pH changes or a low pH.

Killing off Trichodina and other parasites can be accomplished with salt in many instances. Flukes can be controlled by the use of Aqua Prazi

Update: Because of the over use or salt, there are now many “salt resistant” parasites. The NEW recommended treatment would be TERMINATE which is made to treat “salt resistant” parasites including costia.

Back to top

Koi Body is rough, no slime coat
Sandpaper skin is usually secondary to a bacterial infection and "rough skin" usually means the fish has pretty much "had it" and the body is shutting down. A reasonably healthy fish with imune system "on line" can generate a slime coat as fast as parasites can chew it off. When a fish is about to "check out" they lose this resilience and the sandpaper skin is the result.

Still, certain parasites can cause sandpaper skin, such as Costia and Chilodonella. These parasites are tough. Costia sometimes resists salt treatments. The problem is then that you might need potassium permanganate or Formalin for these parasites and then, those treatments are really tough on a fish who's already under the maximum stress.

Update: The new treatment for Salt Resistant Parasites is: TERMINATE

Also, crazy people who use Potassium or Formalin, or Salt as a stiff short term bath treatment can also burn off the slime coat. The fish has still basically "had it" but at least you can be satisfied that you did it yourself and that if you'd just leave the rest of the fish alone they'll be fine.

You can attempt to save such fish by injecting them with antibiotics. For some reason, saltless water with A LOT of live plant matter also seems very helpful if you're sure there's no need for salt. (Salt and plants don't generally mix) - What I usually will do, once I am sure there are no parasites, is remove the sandpaper fish to a clearwater vat with a lot of aeration and then put so much Parrots Feather in there that the fish pretty much has to wend it's way like a snake through the strands.

The other fish should be salted to no more than 0.3% and fed medicated koi food to stave off any infection they were about to succumb to.

Update: Because of the over use or salt, there are now many “salt resistant” parasites. The NEW recommended treatment would be TERMINATE which is made to treat “salt resistant” parasites including costia.

Action Items

+ Any time fish have an infection, you should realize that all the other fish have been exposed to the same conditions and infectious agents that caused the visible disease in the ones you're looking at. This makes it wise to feed EVERYONE in the collection a medicated koi food. You can do this for fish with Anchor Worm and Fish Lice to prevent the bitewounds from those parasites from going on and getting infected.
+ The first thing you should do is test your water for all the important nitrogen and pH parameters. A too-low pH is a common cause of most of the above.
+ Next, you should salt those fish if possible. Even if this is not curative, it will help reduce the stress the fish are under, reduce the amount of water entering the wounds, or even enhance the effects of some of the other recommended medicines.
+ Do not overmedicate. You should seriously consider simply testing the water, salting the pond, and applying Aqua Prazi and a medicated koi food as a good starting point in most of the above cases.
+ If you can see a parasite or other creature attacking your fish, particularly Anchor Worm and Fish Lice, you can annihilate it with Diflubenzuron (Click here)

Needed or Recommended Items

+ Water tests Kits
+ Diflubenzuron for Anchor Worm or Fish Lice.
+ Medicated koi food
Aqua Prazi for Flukes