Koi Parasites


Many thanks to Sacramento Koi for the following information on Koi parasites.


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Parasites:  Parasites are a real health issue when it comes to koi fish. The most common way koi fish contact parasites is from other fish. Before a new koi is introduced to the pond, it is extremely important that the new fish be quarantined for 3 weeks. During this time period the koi should be treated for parasites. Isolating a koi for 3 weeks in a quarantine tank, without treating the koi, is no assurance that the koi is parasite free. All that tells you is that if it has parasites, there are not enough of them to make it sick at this time. If you do not have a separate quarantine tank in which to treat a new koi in, then be very careful who you purchase your new koi from. Make sure the dealer is very conscientious about treating all their koi to make sure they are parasite free before they sell them. Do not take their word for it that they are parasite free. Ask them exactly how they treat their koi for parasites. If they are vague about how they treat the fish you would do well to assume the koi will have parasites and then make your decision as to whether or not to purchase the koi based on that fact.

The five most common parasites that affect koi fish are: flukes, costia, chilodinella, trichodina and ich. All of these parasites are microscopic which means you cannot see them without the aid of a microscope. The most common signs that you may have parasites are:

  • Fish are flashing. Flashing is when a fish swims slowly near the side or bottom of the pond and then quickly swims off by first rubbing it’s side against the pond wall.

  • A fish is isolating itself from the other fish.

  • One or more fish have stopped eating.

  • A fish spends much of the time near the water fall gasping for air.

  • Fish are sitting on the bottom of the pond with their fins clamped close to their body or are drifting in the pond with their head pointed upward or downward for several minutes at a time.

  • Sores developing on the fishes body or fins.

  • Fish are dying.

When selecting a treatment to rid koi of a particular parasite, you should always try to select a treatment that will effectively kill the parasite, while at the same time, cause the least amount of stress to the koi. Stress is a real factor that needs to be considered in treating koi. Think of it this way. You can live and work around all sorts of germs and never get sick. Then things change at work and you are suddenly required to work very long hours for several days in a row. Now, when you can least afford it you get a cold. Why is that? It is because your immune system has failed due to the extra stress of working so much. It works the same way with koi fish. When they get stressed their immune system can begin to fail them and any hope for recovery will be slowed down, if in fact they recover at all. An infestation of parasites can be very stressful to a koi.  For this reason, it is very important when treating a koi with parasites to select a treatment that will not stress them anymore than is necessary.

Proper treatment for parasites depends on which parasite the koi have. If you have access to a microscope, by simply taking a scraping from the fish and examining it under the microscope, you can usually tell exactly which parasites are present and then treat for them accordingly. If you do not have a microscope and are looking for one, there is a very good microscope for the price at www.unico1.com  The model M-250  sells for about $500.00.

There are some links below for video of what these parasites look like at 100x magnification.

Suggested Medication for treatment




Bypass Filtration?

(Click HERE for video)
Supaverm - For use on koi only
- Kills Goldfish and several other species
Not necessary
(Click HERE for video)
ProForm-C - Do not use with salt level above .1%
- Will kill most pond plants
- Keep pond well oxygenated
(Click HERE for video)
Salt - Will kill most pond plants Not necessary

Suggested Treatment Procedure


Supaverm is safe for use on koi only. It will kill goldfish! It is believed to remain in the water after use for up to one month. It will not harm the filter media. Remember to shake the bottle well before use. Treat the pond with 1 ml per 100 gallons. Do not perform any water changes for at least 10 days. Supaverm has been shown to be much more effective when used with a salt level of .3% or higher. For that reason we highly recommend using it with salt. If there are plants in the pond and the use of salt is not possible, we recommend treating a second time 5 days later. It is not necessary to do a water change after using Supaverm.       

ProForm-C should not be used when the salt level in the pond is higher than .1% unless you know for a fact that the pond water is very soft. If the pond water is hard at all and the salt level is above .1%, the use of formalin can severely burn the gills of the koi. ProForm-C can kill the beneficial bacteria in the biological filter, so if possible, the filter should be bypassed for at least 8 hours during use. ProForm-C can kill plants so, if possible, all plants should be removed while the pond is being treated and the plants should be treated with potassium permanganate separately before returned to the pond. (To treat pond plants for parasites mix up a solution of 3 tablespoons of potassium permanganate dissolved in 12 gallons of water. Allow the plant’s root ball to dry out slightly and then completely submerge the plant root system in the solution for 2 hours.)

  • To treat ponds up to 1500 gallons  Measure out enough ProForm-C to treat the whole pond at a dosage of 10 ml per 100 gallons. Drain 50% of the water out of the pond and then add the ProForm-C to the pond. After 2 hours refill the pond as fast as possible to its normal level. You must be able to refill the pond within 45 minutes or you risk the chance of burning the fishes gills. Perform this treatment 3 days in a row. If you have costia we recommend treating one more time on day 5. If the pond is being refilled with city water remember to add dechlorinator to the water to remove any chlorine in the new water. This technique is very effective because the parasites are exposed to twice the dose of medication for 2 hours which is usually enough to kill them.

  • To treat ponds over 1500 gallons  The above treatment cannot usually be performed on ponds over 1500 gallons because it takes too long to refill the larger ponds. In this case we recommend performing a 25% water change before each treatment. After the pond is refilled to it’s normal level, add the ProForm-C at  a dose of 12 ml per 100 gallons. Treat the pond 3 days in a row. If you have costia we recommend treating one more time on day 5.  If the pond is being refilled with city water remember to add dechlorinator to the water to remove any chlorine in the new water.

Salt when used to treat for ich should be added at a rate of 1 pound per 100 gallons of water each day until the pond reaches .4% salt. If there is no salt in the pond to start with, this will take 4 days to reach .4%. A 1000 gallon pond will require 40 pounds of salt to reach a salt level of .4%. This may sound like a lot of salt but if you add it over a 4 day period it will not bother the fish. Leave the salt level at .4% for at least 3 weeks. Ich is easily killed with salt when it come out from under the fish’s scale, however it’s life cycle is such that it could take up to 3 weeks to come out and be exposed to the salt water. You can purchase 50 pound bags of “solar salt” at Home Depot for around $3.00 each. Use the cheapest salt you can find because it will have no additives in it which could be harmful to the koi.


 What if you do not know what parasites your koi may have?

The following is a treatment procedure that we use at Sacramento Koi every time we get new koi. This procedure is designed to kill all five parasites in case they are present.

Day 1   Treat the pond with ProForm-C
Day 2  Second treatment of ProForm-C
Day 3  Third treatment of ProForm-C
Day 5  Forth treatment of ProForm-C
Day 6  Add salt to increase pond salt level to .1%
Day 7  Add salt to increase pond salt level to .2%
Day 8  Add salt to increase pond salt level to .3% and add  full dose of Supaverm
Day 9  Add salt to increase pond salt level to .4%
Day 21 the koi should be totally parasite free.

 Sample Treatment Schedule Worksheet

 *Click on schedule to print out a blank treatment schedule worksheet!

Optional Treatment-Potassium Permanganate A very effective alternative to ProForm-C which many people have had very good success with is Potassium permanganate, but it is much more dangerous than ProForm-C and is more complicated to use. Potassium permanganate is an oxidizing agent which means, that to kill the parasites it must first oxidize most, if not all, of the organic material in the pond. For that reason it is hard to recommend a proper dose for a pond unless you know how much organic matter is in the pond. The proper starting dose for a pond that is very dirty will kill the fish in a pond that is extremely clean. The end results that you are trying to achieve is to have the level of oxidation in the pond high enough and for a long enough period of time to kill the parasites, without killing the fish. This is not really easy, but it can be done very successfully if you pay attention to what you are doing. The following is the technique that we have tried and found to be successful:

  • Remove all plants from the pond.

  • Remove as much leaves or debris from the pond bottom as possible.

  • Empty all skimmer baskets.

  • Turn off ultraviolet light.

  • Bypass the biological filter. If you cannot bypass your biological filter, do not use this process. Potassium permanganate will kill all the good bacteria in your filter, which will cause serious water quality problems.

  • Sunlight tends to break down potassium permanganate, so if you can begin the treatment after the direct sunlight is off the pond it can be helpful.

  • The standard  initial treatment dose is 1 level teaspoon per 600 gallons of pond water. If the pond is extremely dirty you can increase this dose by 50%. If the pond is brand new and has very little algae growth, you might reduce the dose by 25%.

  • Potassium permanganate is very toxic. Do not breathe it or get it on your skin.

  • Salt pond to .3%

  • Have some Hydrogen Peroxide on hand in case you need to neutralize it. You can find it in most grocery or drug stores.

Potassium permanganate treatment:   Potassium permanganate consumes large quantities of oxygen during the treatment so make sure the pump to the waterfall is running at all times and add some air stones if you suspect the oxygen level may be low.  When potassium permanganate is added to the water it will turn the pond a bright purple. As long as the water is a “Pink Champagne” color it is active and is oxidizing any organic mater in the pond including parasites. When it turns to a yellow “Tea” color is has been used up and is no longer oxidizing anything. By scooping up a sample of the water in a white ceramic or plastic cup it will makes it much easier to tell when the water changes color. 

        Day 1- Add the proper dose of potassium permanganate to the pond. Note the time it takes to change color. As soon as it changes to a tea color you can stop bypassing the filter.

        Day 2- Add the proper dose of potassium permanganate to the pond. Note the time it takes to change color. As soon as it changes to a tea color you can stop bypassing the filter.

  • Continue to treat the pond each day until the pond stays “Pink” for at least 8 hours at one time. Skip one day and then treat the pond one more time except reduce the dose of potassium permanganate by 20%. After the pond has stayed “Pink” for the second 8 hour period, neutralize the pond with Hydrogen Peroxide at a rate of approximately one quart for every 2,000 gallons. Within 30 minutes the water should be very clear. Perform a 40% water change and you should have parasite free fish swimming in very clean water. The only exception may be ich. If you suspect ich you should replace the salt lost durring the water change and maintain it for an additional 10 days. Do not forget to add dechlorinator to the new water.

    Note: If at anytime during the treatment the water gets so cloudy that you cannot see your fish and you get concerned, you can neutralize the potassium permanganate and make the water clear by adding Hydrogen Peroxide, but if you choose to add Hydrogen Peroxide at anytime during the treatment you will need to wait 3 full days for the Hydrogen Peroxide to evaporate before you restart the treatment.

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