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How to Treat Koi With Potassium Permanganate

Updated July 19, 2017

Potassium permanganate, also known as KMnO4, is an oxidiser that is used in treating flukes, parasites, fungi, protozoans and bacterial infections in koi fish and ponds. If you notice that your koi have skin ulcers, gill disease, protozoan parasites, or are suffering due to poor water quality, potassium permanganate may be an effective treatment for your fish. It can also be used to improve water clarity by oxidising dissolved organic matter in the water.

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  1. Disconnect or bypass any biological filtration connected to your pond or fish tank. Potassium permanganate will kill almost all bacteria (99.9%) that it comes into contact with and will ruin the beneficial bacteria colony in your filter.

  2. Aerate your pond or tank with a bubbler or non-biological filter. Good aeration is necessary because potassium permanganate lowers oxygen levels.

  3. Measure out the dosage of potassium permanganate based on label directions according to your pond or tank's water content. You'll need about one teaspoon per 1,000 gallons. Make sure the teaspoon is level and do not overdose.

  4. Fill a bucket with the pond or tank water and mix in your pre-measured dose of potassium permanganate. Be sure to mix thoroughly.

  5. Slowly add the water containing the potassium permanganate back to the pond or tank. Do not pour the water directly onto any of your fish. Treat for approximately five hours.

  6. Check the water's colour. If it is still pink, pour two cups per 1,000 gallons of 3% hydrogen peroxide into your pond or tank to neutralise and deactivate the potassium permanganate. Do not pour directly on your fish.

  7. Restart your biological filtration system after three hours.

  8. Tip

    You will probably need to treat more than once, depending on the ailment. Follow label directions carefully. Check the water's colour often to make sure the potassium permanganate is still active during your treatment time. The water will turn pink while treating. This is normal and means the potassium permanganate is active. If the water turns brown before five hours has elapsed, you may want to treat again. Follow your product's guidelines. Wait until the treatment is complete to feed your fish, or feed before you begin to avoid ingestion of the potassium permanganate.


    Potassium permanganate can kill your fish, so avoid overdose at all costs. It is toxic above four parts per million. It is better to underdose than overdose. If you notice any signs of distress in your fish such as gasping for air or if any fish die, deactivate the potassium permanganate immediately. Use hand protection when using potassium permanganate because it can stain your hands brown with direct skin contact.

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Things You'll Need

  • Potassium permanganate
  • Measuring cup
  • Measuring teaspoon
  • Mixing bucket
  • Hydrogen peroxide, 3% solution

About the Author

Alana Grelyak is a writer and musician living in Chicago, Illinois. Grelyak earned a Master's Degree in music from the University of Wisconsin, and has written on the topics of entertainment, restaurants, music, telecommunications, and more. Her work has appeared in numerous places, including Punchline, Lumino Magazine, Time Out Chicago, Midwest Beat, Pipeline, and others.

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