Parasites - Chilodonella

The Chilodonella fish parasite is a microscopic parasite at all life stages, so you won’t be able to see them on your fish with the naked eye. They will attach to your pets on the skin, gills or fins. 

Chilodinella fish parasites can cause havoc in a koi pond at any time of the year but is most prevalent in the spring, or cool water temperatures. Their optimum temperature is 40⁰-50⁰ F (5⁰-10⁰C). Left untreated; Chilodonella can kill a lot of koi in a small amount of time.

The Chilodonella fish parasite is round to heart-shaped organism that is full of tiny bubbles. It resembles an onion with tiny roots on one end. It punctures and feeds on the skin of its host to feed leaving behind tiny abrasions where bacteria can enter and cause secondary infections on koi and goldfish. Many times fish suffering with Chilodonella will rub or scrape pond edges in an effort to rid them, but instead cause more damage.

What are the symptoms of Chilodonella on koi?

If you have Chilodonella on koi in your pond you will notice the fish acting itchy or flashing and definitely being lethargic. Many times infected koi will lie on their side on the pond bottom, and then quickly turn upright when startled.


Chilodonella can be treated with Chloramine-Tor malachite green and formalin. Pond Salt can be used to control Chilodonella, either as a pond treatment or a bath, the rate of which will depend upon the stage of infection. If opting to use salt as a pond treatment, be sure not to use medication such as PP or Formalin until the salt has been removed.

Malachite Green (MG) and Formalin (F) Not to be used below 13̊C MG 2% 10ml per 176 UK gallons F 30% at 10ml per 140/150 UK gallons 

Chloramine T *Kusuri* 15-20 grams per 1000 gallons for 4 doses. Not effective in temps below 11̊C. 

• Salt Remember NOT to use salt if Formalin or PP is in the pond already. Use an accurate salt meter to ensure the percentage or ppt is safe. 0.3% starting dose to slowly increase to 0.6% over 24 hours. Any further salt increases should be done slowly. Bear in mind that Trichodina also thrives in marine environments. 
*Remove any Zeolite from the filters as the salt will release ammonia from it. Keeping on top of pond and filter maintenance will help reduce the occurrences.

• Potassium Permanganate

Pond treatment for parasites and snails: 2-4 g / 1000 liters.
Keep on adding in small doses of 2g/1000 litre to keep the pond water pink for 1-2 hours

Pond treatment for bacteria and ulcers: 2-4 g /1000 liter
Keep on adding in small doses 2g/1000 litre to keep the pond water pink for 8-10 hours

Dip:  very effective for parasites, bacteria, ulcerations etc. Use 1 gram per 10 liter water for 7 minutes. Always aerate and ALWAYS remove the fish if it gets restless and jumpy. Control timing precisely and do not treat too many fish at the same time unless you can time the treatment of each fish correctly.

This treatment tough, can push an ailing fish ‘over the edge’. Therefore fish already weakened by disease should first be treated with a 30-50% dose first time. Alternatively simply shorten you dipping to 1-2 minutes if the gills are infected and necrotic.

Important. Always de-clog the gills with a Peroxide (hydrogen peroxide) treatment to the pond. It not only terminate the action of the potassium permanganate, but will clear the water from the brown colour. Will also aid in removing the brown coloured necrotic tissue from the gills. 


I want to warn about use with salt. Salt (NaCl) is additive to potassium permanganate. To strip parasites from basically HEALTHY FISH can be tolerated, but sick, weakened fish should never be subjected to such treatment and will surely die. Always test salt level or ask the pond owner about his salt regimen before deciding on the protocol for the potassium permanganate treatment.

For certain phenotypes of the Doitsu koi the uptake of oxygen is poorer for certain physiological reasons. They stress more quickly and die due to oxygen starvation. Use half the recommended dose/time when dipping the first time at least to determine their suitability for the treatment..

Any treatments added are done so at your own risk. It is your responsibility to know your pond volume and to calculate dosages correctly. 

Golden Rules Of Treating Koi

Scrape the Koi first before treatment

Identify which Parasite is causing the problem before treatment

Make sure the pond water is salt-free because it can harm Koi when used with most chemicals

> Calculate the Volume of Water accurately

Turn off the UV Unit when treating your Pond

Test your Water Parameters before Treatment

> Follow the label’s instructions and do not overdose. Chemicals can cause serious damage to your Koi if amounts are miscalculated