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Koi Parasite Treatment

Help, I Have a Parasite in my Pond! Choosing The Correct Koi Parasite Treatment

Finding a parasite in your pond can be a major concern and can quickly harm or even kill your valued fish. If any of your fish become infected is important that you treat the condition quickly, selecting the correct koi parasite treatment for your situation.

Many parasites cannot be seen with the naked eye, so to accurately identify and eradicate them we recommend having a microscope available to carry out a scrape. 

Parasites And Choosing The Correct Koi Treatment


Trichodina (or 'Trich' as we call it for short) is one of the parasites that you’ll need a microscope to see, but once you have a scrape on the slide it is one of the simplest to detect. This parasite appears as a perfectly round shape, with small hooks which constantly revolve and are the cause of the damage to your koi. If left, Trich can quickly cause major damage to the skin and gill tissue.

One of the most effective treatments to use to deal with Trichodina is Potassium Permanganate – a powdered chemical which is highly effective against a range of koi parasites and can also be used as a disinfectant.

When using Potassium Permanganate I would always recommend having a neutralising solution such as Hydrogen Peroxide to hand and ensuring that you follow the instructions on the product packaging.


White Spot

Often referred to as Ich/Itch/Ick, White Spot is caused by the Ichthyophthirius parasite and appears as small white spots between 0.1mm and 1mm on the body, tail and fins of a fish. This nasty parasite can quickly spread through a pond infecting all of koi in it, and if left untreated can kill many fish in a short period of time.

White Spot can be treated by a selection of koi parasite treatments, depending on if you prefer one particular manufacturer over another:


Gill and Skin Flukes

Gill and Skin Flukes are egg laying flukes, and under a microscope can be identified by the large hook they use to attach themselves to the fish. All fluke product manufacturers recommend using at least two doses, our intention is not to use the same koi treatment every time.

In stubborn cases Colombo Lernex Pro is advised, but should not be used as the initial product you try to rid your pond of this tricky koi parasite.

In addition I will sometimes use a dose of Potassium Permanganate 24 hours before using any Fluke treatments.



Chilodonella is another parasite which will affect the skin and gills of a koi. Under the microscope it appears as an oval or leaf type shape and moves at a fairly slow speed so can be tricky to spot.

Whilst it can be treated with any of the dye based treatments such as Evolution Aqua FMG, Colombo Alparex (marketed for invisible parasites) or Potassium Permanganate, my recommended choice is Colombo Alparex.



Costia is possibly the hardest parasite to find on a microscopic sample, but one of the most deadly if left unchecked. It moves much faster than Chilodonella and under the microscope you can spot the characteristic flicking of its curved body.

From my experience it can be spotted at 40x magnification, but I recommend at least 100x magnification if you have not seen this parasite before. Like Chilodonella, Costia can be treated with the same range of dye based koi treatment products.


Keeping an Eye on Your Pond

One of the most important things you should do as a koi keeper is to watch your fish.

This may sound like an obvious thing to do, but by watching your fish closely you not only get added enjoyment from your pond, but you can also quickly spot any changes in the way your koi are acting and get an early warning of any changes in your pond environment.

Look out for fish chafing their skin on plants or rocks, or sometimes rocking backwards and forwards in the water as this can be a sign that a parasite is present.


A word of warning

No matter which koi parasite treatment you use, you should always follow the product safety guidelines and usage/dosage instructions. It is also essential to check your water parameters, adjusting as necessary before using any koi parasite treatment.

As with many treatments, the effectiveness can vary according to your pond conditions and environment. If in doubt please get in touch and a member of our team will be happy to provide professional advice.

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