Keeping your koi free from disease is the aim of every koi keeper. However it is inevitable that at some time your koi will suffer from ill health and will need to be treated. The information here will give a brief guide to the most common ailments koi suffer from and the best way to treat them.

In this article we will give an introduction to the most common parasites that koi are susceptible to.


It is almost impossible to keep your koi 100% free from all parasites. To a healthy koi a few parasites will not cause any problem, but a weak koi or one that is kept in crowded conditions or poor quality water will be susceptible to a parasite infestation. The most common parasites that you will find are costia, white spot, trichodina, chilodonella, flukes, anchor worm and carp lice.

Common symptoms of a parasite infestation are fin clamping, flashing or scratching, jumping out of the water, excess mucus being produced and gasping for air. Unfortunately there is no single treatment which will be effective against all parasites and apart from anchor worm and carp lice which can be seen with the naked eye, you will need to take a skin scrape and use a microscope to identify which parasite you have so you can choose the correct treatment. Most people will not have access to a microscope or may be uncomfortable using one, however most koi dealers will be more than happy to help. You will need to take one of your fish along and the dealer will check them for you. Please be aware it is pointless taking a dead fish along to a dealer for any reason, he is unlikely to be able to detect anything that would be of any use.

Once you have identified the problem the treatment is pretty simple, you may need some accurate scales to measure out some of the treatments as they may come in powder form.

    • White Spot – treat with a formalin malachite mix, use a mix designed for use with koi and carefully follow the manufacturers guide as to the dosage, you need to give 3 treatments due to the life cycle of white spot. The time between each treatment will vary according to the temperature
    • Costia – treat with potassium permanganate, again buy from a koi dealer and carefully follow the dosage instructions
    • Chilodonella – treat with a formalin malachite mix, one treatment should be enough
    • Trichodina – one dose of potassium permanganate
  • Flukes – treat with flubendazole, you will need to buy from a koi dealer, again follow dosage carefully

Do not be tempted to treat your koi for parasites without knowing exactly what you are treating them for, over use of these treatments will make them less effective in the future. The reason I have not stated recommended dosages is that the medications can be made to different strengths depending on the manufacturer, if you don’t use enough you will not solve the problem and it may become harder to treat in the future and if you over dose you may harm or even kill your koi.

The key to keeping healthy koi is not to overcrowd as too may koi in a pond, no matter how good the filtration system will lead to ill health. Water quality is key to healthy koi.

Visit our website and view the koi treatments we have available.

Mark Huyton is a keen koi keeper, having kept koi for over 20 years he opened a retail unit in the late 1990s providing a wide range of koi which he imported direct from Japan. With a wealth of knowledge built up over the years he is more than happy to pass on his experience and help fellow koi keepers when ever he can. You can visit his website and find out more about the koi treaments which are available.

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Originally posted 2015-08-22 09:38:47.