All animals, even those from the same species, can react differently to different stressors in their environment. If any of your Koi are looking unhappy then this is the procedure that you should follow in order to determine what the problem may be and how to deal with it. (See also our guide on Koi keeping basics).
This information applies to Koi only. If you have other fish species in your pond, please check that any treatments recommended are suitable for them also.
Signs that your Koi may have a health issue:
Jumping, sitting on the bottom with fins clamped in, twitching fins, swimming erratically, laying on the bottom on their side, floating on the surface of the water, rubbing themselves on the sides or bottom of the pond (flashing), sulking at the bottom of the pond, hanging mid water, gasping on the surface of the water, irregular gill movements, ulcers, redness of the skin or fins, fungus on the skin, excess mucus, scales developing a pine cone effect. (1)
If your Koi are suffering, don’t wait, act immediately.
Use a test kit to check that your pH, ammonia and nitrite levels are safe. (This assumes that you are already using a filter to treat the water that goes into your pond to take out chlorine and chloramine). (2)
Water quality
*You can find water quality reports online from your local water company including what the chemical makeup of your source water is. Find your local supplier here: www.discoverwater.co.uk
Ammonia
A safe Ammonia level is 0.02 mg/l or less (3)
If Ammonia is high, carry out a water change to bring it down and then cut down on feeding. Check the level before you feed your Koi, not just after. (Ammonia chemically burns the fish).
Note: test your source/tap water first. If ammonia at source is high, run your water more slowly through your purifier when carrying out water changes.
Further reading: Practical Fishkeeping FAQ on Ammonia
Nitrite
A safe Nitrite level is 0.2 mg/l or less (4,5)
If Nitrite is high, carry out a water change until the level is safe. If the high level persists because the filter is not mature, you may add salt to at 0.75%. As the nitrite level reduces, slowly reduce the level of salt with your regular weekly water changes. (Nitrite suffocates the fish by not allowing oxygen to get to the fish’s blood. Salt at this level allows the oxygen through).
See our article When and How to use Salt for more information.
Further reading: Practical Fishkeeping FAQ on Nitrite
pH
A safe level is 7.0 but the optimum pH for carp is 7.5 – 8.0
If pH is low, carry out a water change until the level is safe.
(Bring the level up to 7 and hold it there for a couple of days, before raising it further, in order to give your Koi time to adapt to the change).
A pH level of 7.0 is safe but below this the water becomes increasingly more acidic and the risk of a pH crash increases. A pH crash is the point at which the bacteria in the filter have used up the bicarbonate, already existing in the water, that they need to survive. They are no longer able to treat the ammonia and nitrite that accumulate, and this rapid accumulation becomes toxic to your fish. (6,7)
Further reading: Practical Fishkeeping FAQ on pH
Oxygen depletion
This can be prevented by keeping your pond clean of organic debris, with regular weekly water changes and by providing sufficient aeration. (8)
Regular weekly water changes of 10-20% will help to maintain a healthy balance in your pond.
If all water test readings are as they should be, but your Koi are still not happy:
Parasites
Carry out a skin scrape and examine mucus samples under a microscope from four different fish to find out if they have a parasite infestation.
Fish normally carry the odd parasite on their body without any ill effects, however, under certain conditions, such as when the fish is stressed, water quality is poor, or the environment is dirty, parasites can multiply until the fish becomes infested and unwell as a result. Should an infestation be identified, it is not just an individual fish that will need to be treated, but the whole pond along with the whole community of Koi in the pond.
Equipment needed:
Slides
Bowl or floating basket for holding your Koi whilst carrying out a scrape
A good Koi Health book with pictures and descriptions of Koi parasites
Once you have identified which parasite you have, treat it accordingly. (9)
Common parasites and their treatment
Trichodina (10)
Treatment: Malachite and Formalin
(We recommend using separate bottles of Formalin and Malachite Green rather than blends as blends can often be weaker than is needed).
Dosage: Follow the instructions on the bottles (not suitable for use at low temperatures).
Costia (11)
Treatment: Formalin and Malachite Green
(We recommend using separate bottles of Formalin and Malachite Green rather than blends as blends can often be weaker than is needed).
Dosage: Follow the instructions on the bottles (not suitable for use at low temperatures).
Alternatively (not to be used in conjunction with Formalin and Malachite Green)
Dosage: 0.9% (use a salt meter) in the pond and maintain that level for one week before slowly reducing with your regular weekly water changes. (You can use salt one week after dosing with Formalin and Malachite Green).
See our article When and How to use Salt for more information.
White Spot (12)
Treatment: Formalin and Malachite Green
(We recommend using separate bottles of Formalin and Malachite Green rather than blends as blends can often be weaker than is needed).
Dosage: Follow the instructions on the bottle (not suitable for use at low temperatures).
Treat up to 3 times, 7 days apart.
Alternatively (not to be used in conjunction with Formalin and Malachite Green)
At 0.75% (use a salt meter) in the pond and maintained at that level continuously for six weeks before reducing slowly with weekly water changes.
See our article When and How to use Salt for more information.
Chilodonella (13)
Treatment: Formalin and Malachite Green
(We recommend using separate bottles of Formalin and Malachite Green rather than blends as blends can often be weaker than is needed).
Dosage: Follow the instructions on the bottle (not suitable for use at low temperatures).
Gill Flukes (14)
Treatment: Flukesolve
Dosage: Follow the instructions on the packet
Body Flukes (15)
Treatment: Flukesolve
Dosage: Follow the instructions on the packet
Parasite infestations often occur in ponds which are poorly maintained, where the fish become stressed, and where areas of waste have been allowed to build up in the system. Making sure your pond stays clean at all times will reduce the number of parasite outbreaks that occur.
Fungus
This is a secondary infection. The fungus grows in an open wound and is a sign of poor husbandry and dirty water.
Saprolegnia (cotton wool disease)
Treatment: Formalin and Malachite Green
(We recommend using separate bottles of Formalin and Malachite Green rather than blends as blends can often be weaker than is needed).
Dosage: Follow the instructions on the bottle. (not suitable for use at low temperatures).
Diseases that are neither as a direct result of poor water quality or parasite infestation can include:
Viruses and bacteria
Virus
Koi Herpes Virus (KHV) can be dormant in carrier fish until they undergo some kind of stress, at temperatures over 18 degrees C, which can then trigger an outbreak which will affect naïve fish. The mortality rate is high, and survivors become carriers. (16)
Treatment: None
Carp Edema Virus (CEV – also called Sleepy Disease) can remain dormant in carrier fish and can infect naive fish that come into contact with carriers. Treatment with salt is highly effective if carried out promptly but mortalities can be high if not. (17)
Treatment: PDV Salt
Dosage: 0.5% (use a salt meter) in the pond and maintain that level for one week before slowly reducing with your regular weekly water changes. If symptoms return as the salt level is reduced, raise it back up to 0.5% and repeat.
See our article When and How to use Salt for more information.
Bacteria
Bacterial infections can be introduced with a new fish that has an existing bacterial disease which then spreads to other fish, or it can occur in a pond that has not been correctly maintained and where areas of waste have been allowed to build up and create a breeding ground for bad bacteria. Bacteria can also attack fish whose external immune system has been compromised by the overuse of chemical treatments.
Treatment will involve the use of antibiotics that can only be prescribed by a vet.
If you are unable to effectively diagnose and treat sick fish yourself, contact a Koi health professional who can visit your pond, carry out a full investigation and devise a treatment plan.
Recommended Koi Health Specialists
Kevin Unger (Koi Valley)
07770 368995 (Midlands with national coverage).
kevin@koivalley.co.uk
Des Harris (Koi Health and Pond Care)
https://koihealthandpondcare.co.uk/
tel:01474 702818 (Kent area)
Dean DiMarco - The Koi Clinic
https://www.thekoiclinic.co.uk/
07861 734223
(Tyne & Wear, Co. Durham, Teesside, Yorkshire and Cumbria)
Matthew French - Aquatic Management Services
https://aquaticmanagement.co.uk/domestic/domestic-pond-management/
01793 700241
07786 083458
(based in Swindon)
Other Koi health specialists are available and can be found by entering “koi health specialist” into a search engine.
If you would like to talk to a fellow hobbyist, Shaun Slevin is very knowledgeable and is always willing to give free advice. He also runs a Facebook Group called Koi Helpline UK.
His number is 07518 384548
For a list of vets who are happy to treat pet fish, visit the Fish Veterinary Society
Prevention is better than cure
What Koi keepers can do to prevent disease
Know and understand diseases and how to treat them.
Use good pond and filtration design
Study and understand the behaviour of their Koi in order to recognise signs of deteriorating health before it becomes a problem.
Know the exact volume of your pond so that you don’t over or under dose medications. (You can use salt to work out the volume of your pond – see our article When and How to Use Salt for more information).
Use good practice and husbandry
Maintain bio-security
Equipment
Water test kit (to test pH, kH, Ammonia, Nitrite, Nitrate and oxygen – API and Tetra are both manufacturers of basic test kits that you can use, or you can use digital meters which, while more expensive, give a more accurate reading)
Chlorine filter
Good Koi health book
Viewing bowl or floating basket
Medicines to have on hand:
PDV salt (enough to treat your pond to 0.9%)
Related links that you may find interesting:
- https://hanoverkoifarms.com/koi-symptom-diagnosis/
- https://apifishcare.co.uk/product/freshwater-master-test-kit
- https://ornamentalfish.org/wp-content/uploads/2012/08/Water-Quality-Criteria.pdf
- https://ornamentalfish.org/wp-content/uploads/2012/08/Water-Quality-Criteria.pdf
- https://cuttlebrookkoifarm.co.uk/understanding-nitrite/
- Survival and Growth of Common Carp exposed to different water pH levels
- pH crash
- Dissolved oxygen levels in tanks
-
Fish parasites under the microscope Ich, Trich, Costia, Chilodonella, Flukes and Argulus.
- Cuttlebrook video of Costia
- https://fishpathogens.net/pathogen/ich-whitespot-disease
- https://fishpathogens.net/pathogen/chilodonella
- Cuttlebrook video of Gill Flukes
- Cuttlebrook video of Skin Flukes
- https://fishpathogens.net/pathogen/khv-koi-herpesvirus
- https://www.pondtrademag.com/language-of-koi-treating-koi-sleeping-disease/
- https://www.practicalfishkeeping.co.uk/features/frequently-asked-questions-on-using-salt/