Koi Doctor

Koi Doctor

Koi Diagnosis and Treatments

Koi are no different to humans when it comes to illness and diseases. Although Koi are generally tough and hardy creatures, they too are susceptible to illness if the ideal conditions are not maintained. These are some guidelines on how to recognize the symptoms and how to go about diagnosing and treating your fish.
The possible causes of ailments in Koi are:

  • Water quality
  • Physical injury
  • Protozoan parasites
  • Tremetode parasites
  • Crustacean parasites
  • Bacterial infection
  • Viral infection



When observing for symptoms it is important to note whether it is only one fish exhibiting a symptom or all of them. If it is only one or a small percentage, chances are the cause might be a disease or parasite. If most or all of them show the same symptoms it is more likely a water quality issue.

Symptom 1: Flashing
The most common symptom. This is when the fish turn sideways while darting in a specific direction, exposing/flashing their sides. Sometimes they are actually scratching/rubbing themselves against an object in the water. Flashing is a sign that something is irritating them. There can be many causes of flashing. The following will help to narrow it down.

Most or all of the fish exhibiting flashing symptom?

  • Possible water quality issue or discomfort due to recent change in water chemistry (partial water changes, rain water entering pond etc.). Check all parameters of good water quality and correct accordingly (PH, Ammonia, Nitrite etc.)
  • Possible irritation due to addition of medication or water treatments. If using treatments, double check the dosage used, and correct using a partial water change if necessary.

Flashing occurs during afternoon or evening only?
Possible fluctuation in PH between morning and evening periods. Fish can tolerate a PH fluctuation of no higher than 0.3. Check PH reading in the morning and evening. If the fluctuation between these periods is higher than 0.3, adjust the kH by adding baking soda. When KH tests over 100 ppm, PH fluctuations will be minimal.

Flashing occurs during of shortly after feeding?
Possible problem with food particles getting stuck in gills. Problem should desist shortly after feeding, but can be prevented by using non-flake type foods or foods with less oils or powdery residue.

Flashing occurs when fish are close to pumps, lights or electrical devices?
Possible stray electrical voltage in the water. Test the water with an electrical meter to determine if any of the wiring in your electrical devices have a short. If not, observe the fish closely as they may simply be using the devices as a scratching post.

Flashing still occurs after eliminating all of the above possibilities?
Protozoan parasites, trematodes or crustacean parasites may be the cause.

  • Protozoan Parasites – Most, but not all protozoan parasites can be slowed down by salt. First try a salt treatment of 0.3% and maintain this for about 2 weeks. If flashing continues you may need to try a stronger treatment such as ProForm C.
  • Trematodes– Most common tramatodes affecting Koi are various types of flukes. For this it is recommended to use Fluke Tabs or Praziquantel.
  • Crustacean Parasites – Most common are fish lice and anchor worms. These are visible to the naked eye, so look for them on the fish before administering treatment. Dimilin is the safest and most effective treatment for this.

Symptom 2: Jumping
In most cases when fish jump out of the water, it is usually for the same reasons as with flashing (ie. Poor water quality or parasites), so follow the steps listed under Flashing. However, newly purchased Koi may sometimes jump as a fright response or while trying to adjust to new water. This can be prevented by properly acclimatizing new fish, and by floating an object on the surface of the water eg. Styrofoam, to give them cover and make them feel more secure.

Symptom 3: Sitting On The Bottom
This is also an indication of poor water quality or parasites. Check all parameters of good water quality and adjust accordingly, and administer treatment if necessary. New and frightened fish may also exhibit this behavior.

Symptom 4: Fins Clamped To Body
Again, this is an indication of poor water quality. Check all parameters of good water quality and adjust accordingly. If water quality is good and symptom persists, only then move on to treatment for parasites.

Symptom 5: Fin Twitching
Rapid twitching of fins are most likely a parasite problem. Follow steps for identifying the parasite and administer treatment accordingly.

Symptom 6: Gasping
This is when the fish continually surface with their mouths open, gulping air. This indicates they are having trouble breathing, and can be caused by any one of the following:

  • Water is low in oxygen.

Observe the time of day the symptom occurs. Warmer water holds less oxygen, so if this behavior occurs when the water is at its warmest, it is possible that low oxygen is the cause. Aerate the water 24/7 to increase oxygen levels.

  • Nitrite Poisoning

Nitrite poisoning damages the gills. Check Nitrite levels. If present, do a 50% water change and add 0.1% salt.

  • Parasites or Bacterial Infections

Continue aeration of the water. Follow steps/treatments listed for parasites. In the case of bacterial infections administer medicated antibiotic food.

Symptom 7: Hanging at the Surface
Fish that stay at the surface can be caused by any of the following:

  • Bacterial Infection

When the fish hangs at the surface with the head pointing down and tail up, and is lethargic and responsive, this is a sign of a serious bacterial infection. The fish needs immediate attention. Most bacterial infections are brought about by other problems such as parasites, so address those issues first and check all water parameters before attempting treatment

  • Low PH

When fish are at the surface with their head pointing up and their tail pointing down, and acting lethargic and listless, this is usually due to low or ph. Check PH and water quality and adjust accordingly. If symptoms persist if may be a sign of parasites.

  • Swim Bladder Problems

When the fish are floating or rolled on their sides and unable to swim below the surface, this is a sign of swim bladder problems. Little is known about the cause of this disorder, but rapid temperature declines, bacterial infections, constipation, and poor diet are believed to be contributing factors. Treatment involves removing affected fish to a shallow tank or container (to avoid stress of trying to swim down) and increasing temperature gradually until it is at upper 70 deg. range. Vary the diet of the affected fish and try to include some antibiotic food. As a last resort, a procedure can be done where a needle with a syringe is inserted into the bladder of the fish through its side and the excess air that keeps the fish afloat is drawn out. This is a simple procedure but can be fatal if done incorrectly.

Symptom 8: Erratic Swimming
Erratic swimming patterns are usually a sign of some sort of toxicity in the water, such as chlorine from water treatment plants, ammonia and heavy metals such as copper or iron. A 50-75% water change is recommended, as well as the use of a commercial water conditioner if using tap water that may contain the above mentioned compounds.

Symptom 9: Isolation
When one fish isolates itself from the others it is usually a sign of a parasitic attack or a bacterial or viral infection. Check all water parameters before treating the affected fish accordingly.

Symptom 10: Red Sores/Ulcers
Red Sores/Ulcers are usually the result of a bacterial infection invading an area previously degraded by parasites. They start as sores and gradually develop into open wounds, and if left untreated the fish may eventually develop dropsy and die. Best method of treatment is to maintain water quality while first addressing parasite problem. Then get rid of the ulcer-causing bacteria (Aeromonas) by heating the water gradually to around 82 deg. After this is achieved, only then can you begin to treat the wound itself, using Debride ointment and/or Iodine.

Symptom 11: White Fuzz
White fuzz growing on spots on the body of the fish can be caused by any one of the following:

  • Saprolegnia (Fungal Infection)

Saprolegnia infections are usually secondary infections that develop on open wounds as a result of other problems such as ulcers or parasites, or when the slime coat has been damaged. Therefore, you need to address initial cause for a complete cure. However, you may treat the area of growth using Debride ointment or Iodine, swabbing firmly enough to remove any growth and dead tissue.

  • Columnaris (Bacterial Infection)

Columnaris is also referred to as cotton-wool disease, mouth rot, fin rot, and saddleback, and is a bacterial infection. Columnaris will quite often infect the mouth, and it can actually cause it to rot. Columnaris is also more likely to show fin damage in addition to the areas infected on the body of the fish. It is recommended to isolate the affected fish in a treatment tank and administer antibiotic treatment such as Tricide-neo.

  • Epistylis

Epistylis is a parasite found in dirty pond water or water with infrequent changes. Growth can be observed on multiple areas of the fish at the same time, as well as reddening of the affected area. This can usually be taken care of using salt treatments of 0.3% and water changes, or ProForm C if  a stronger treatment preferred.

Symptom 12: White Lumps
White lumps growing on the body of the fish can be caused by any one of the following viruses:

  • Carp Pox

Carp Pox appears as smooth, shiny, white or gray lumps on the body of the fish. It is most common in crowded or dirty ponds. There is no known cure, but some people have reported improvement in this condition when water is heated to around upper seventies to low eighties. It is recommended to isolate the affected fish before attempting this treatment.

  • Lymphocystis

This is a harmless virus that appears as rough and wart-like and is usually formed over a previous wound. There is no known cure. However, it is harmless and does not spread easily so there is no need to be overly concerned.

Symptom 13: White Specks
White specks or spots is commonly known as “Ich” (short for Ichthyophthirius, a parasite). This can normally be treated by salt at 0.3% or Proform C if you prefer a stronger treatment.




Remember, prevention is better than cure!
If you take the right approach to maintaining your tank or pond, your Koi should be just fine. Avoid potential health issues arising with your Koi by paying close attention to the following criteria for ideal Koi habitat conditions:


Water Condition

The most common culprit in ailing Koi is poor water quality. Check your PH, ammonia and nitrite levels regularly. Ensure that you have a good filtration system, and never allow the bio filter to backwash into the pond or tank. Partial water changes done regularly can also go a long way in maintaining good water conditions.



Fish breathe oxygen in the water through their gills. Sufficient aeration is crucial to keeping healthy fish. Install an airstone, waterfall or some other form of aeration to ensure that your fish have enough oxygen.



Do not overcrowd your pond or tank, as this places a great deal of stress on your fish as well as on your biological filter. A good rule of thumb for the novice Koi keeper is to aim at keeping around 50 inches (125 cm) of fish per 1000 gallons of water



Make sure that your fish are getting the right nutrition. Never overfeed your fish, as excess food can pollute the water.



Make sure that there is good movement in the water with no “dead” areas with low circulation. Stagnant water is not good as bad bacteria grows well in stagnant water with low oxygen.


Prompt Treatment of Injuries


External injuries can occur from time to time, especially with large Koi. Injured fish should be removed immediately and the wound treated, as open wounds make the fish extremely vulnerable to parasite.