Koi Ich Treatment Guide (Fish Safe Methods)

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How to Treat Koi Ich & Prevent Outbreaks (2022 Updated Guide)

icthyophthirius multifiliis ich parasite that causes koi ich disease
The parasite Ichthyophthirius Multifiliis; the cause of “Ich” disease in Koi. Source: El-Cezerî Journal of Science and Engineering. 2. 47-52.

Ich is a very common problem for many species of fresh water fish, with both koi and goldfish being no exception. Ich presents as small white spots on the scales, fins, or gills of fish which can grow to resemble the appearance of grains of salt all over the body. The appearance of these white specks across the skin of the fish is also why the disease is sometimes called “white spot disease”. At its core, the disease itself is caused by a parasite which latches on to the skin of fish, known scientifically as Ichthyophthirius Multifiliis; hence the shortened name “ich”.

The parasite can be found in many ponds in small quantities, and usually does not present any problems if koi are healthy and water conditions are good. Just like many other diseases and infections, koi become the more susceptible to contraction during periods of stress or lower immune activity. For example, one of the most common times for parasites to infect fish is during their winter hibernation period, as their bodily functions have slowed to a crawl, along with their immune system for fighting back pathogens. Parasites can also become a problem in poor water conditions, after an injury, or if koi are malnourished – all which lead to stress and a weaker immune system.

Even though ich can be very dangerous if left untreated, the disease itself is fairly easy to remedy, especially if caught in the early stages. The main problem with ich is the possibility of further bacterial and viral infections occurring in lesions, which is why it’s important to control at first signs of the disease.

What Does Koi Ich Look Like? Is it Dangerous?

A koi with ich spots from ich disease white spot disease
The ich parasite presents as white hard spots on the scales, fins, and tail of fish. The spots are very small and can resemble grains of white sand. Public domain.

Even if your fish has been infected by an ich parasite, you may not notice until the disease begins to spread and further symptoms present. A single parasite is not much of a concern, but as with all parasites, they’re highly contagious and can reproduce at an alarming rate under the right conditions. In most cases of ich, the first symptoms you will notice are small white spots on the body of your fish. In the early stages these can be hard to find, but as the disease spreads more and more spots will appear and give the appearance of grains of white sand. The little spots can appear anywhere on your koi, but are more common on the bodily scales as this is the easiest place for the parasite to anchor. The spots can also appear along the fins, tail, and even without the gills – which can be particularly dangerous as it can interfere with oxygen absorption.

In-fact, the mortality rate of ich in most species of fish can be associated with respiratory problems that arise from damage to the tissue of the gills. If left to spread uncontrolled, large amounts of cysts begin to cover the gill tissue, greatly reducing oxygen transfer to the blood and increasing the risk of infection. Because of this, all cases of ich, however small, should be treated immediately to reduce the risk of fish death in later stages.

Although the small white specks are the tell-tale sign of ich parasites, koi may also present behavioural symptoms, as well. These include a loss of appetite, swimming alone, hiding under shelters, and also rubbing against pond objects as they try to scratch off the parasites. A list of symptoms can include the following –

Koi Ich Symptoms:

  • Small white spots which resemble grains of sand
  • Rubbing on pond objects
  • Loss of appetite
  • Swimming away from group
  • Hiding under shelters/bottom of pond
  • Lack of color & dull appearance
  • Bacterial or viral infections (i.e., ulcers)

What are the white spots that appear with Ich?

the lifecycle of the ich parasite
Diagram showing the basic life cycle of the ich parasite, including host stage, reproductive stage, and infectious stage. (Click to enlarge) Peter R. Richter, Sebastian M. Strauch, Azizullah Azizullah and Donat-P. Häder, CC BY 4.0, via Wikimedia Commons

The white spots which appear with ich are actually the parasites themselves, having surrounded themselves in a cyst-like shell to feed on bodily fluids in the skin. The parasite goes through several stages in its life-cycle:

1) A free-swimming parasite stage seeking a host (tomite),  2) Encysted stage within skin of host (trophont), 3) Reproductive dividing stage after falling off skin of host (theront), 4) Free-swimming parasite stage seeking new hosts again (tomite).

Depending on water conditions, particularly water temperature, this life cycle can be completed in as quick as 3 days, or as long as 8 weeks. Only in the trophont-stage will you notice visible symptoms, as it’s impossible to see the parasites free-swimming in the pond without a microscope and water sample. Due to their lifecycle duration being heavily reliant on water temperature, we can use this to our advantage when treating the parasite. Instead of treating for several weeks, heating pond water or a quarantine tank will speed up the reproductive process, and allow treatments to work faster as the parasites life-cycle cycle shortens. The ich parasite cannot be treated in its encysted (throphont) stage, so treatment needs to be carried out on the newly spreading parasites free-swimming across the pond system.

What Causes Ich Outbreaks in Koi Ponds?

ich parasite can be transported by herons
Just like many other parasites, ich is commonly brought to ponds by foreign animals, such as predatory birds. Public domain.

Just like other common parasites, the ich parasite is almost always brought to the pond system by foreign animals or objects. Whereas other parasites can lay dormant for a long period of time before becoming a problem, ich parasites rely on extremely fast infection and reproduction to survive. The ich parasite may have been brought to your pond already, but unless it can find a host within 48 hours, it will quickly die off.

In large ponds will low fish stocks, it’s much more difficult for parasites to find hosts, which leads to a much lower rate of infection and reproduction. However, if you have a fairly small pond, or if your pond is heavily stocked with fish, even a single parasite can cause a huge outbreak of ich due to its fast life cycle. In these cases, it’s even more important to have safeguards in place to help prevent parasites from getting into the pond, as it becomes more and more difficult to combat the parasite as the infection spreads.

The single biggest contributor to ich outbreaks is a lack of proper quarantine procedure when introducing new fish to the main pond system. Unlike other parasites which can lay dormant for long periods, ich requires a host to survive more than 48 hours, and any new fish you bring could already be infected with the parasite during its cyst-stage. While in quarantine, you can monitor the fish for symptoms of disease and take actions to treat the fish and water to remove any lingering parasites.

As well as new fish, wildlife, such as herons or ducks, can also carry parasites and pathogens between ponds as they visit your waters. Due to the short life cycle of the ich parasite, contamination in this way is much less common in comparison to the introduction of new fish.

Causes of Ich outbreaks:

  • Lack of quarantine procedure for new fish
  • Visiting predators or pests
  • Sickness, stress or injury
  • Poor water quality & conditions
  • Lack of proper nutrition
  • Poor “winterization” routine

Once the ich parasite is in the pond, its rate of infection is increased during times of stress, sickness, or low immune activity (hibernation/torpor). During these times koi are far more vulnerable to contracting the parasite as their immune systems will be compromised and be unable to fight back infection.

The Best Koi Ich Treatments & Recovery Guide (5-Step Process)

Note:  When using medicines you will need to remove any activated carbon from your filter box and turn off UV clarifiers, as both will interfere with the effectiveness of treatments. For the most effective treatment, fish should ideally be quarantined unless ich has already spread across the entire pond system. Heating water can speed up treatment and the lifecycle of the ich parasite.

quarantine new fish to prevent the spread of ich1) Quarantine New & Infected Fish

When?  At first signs of ich on a single fish, or before introducing new fish or plants to the main pond system.

Prevention is always better than cure, and the easiest way to prevent the ich parasite from entering your pond is to quarantine new fish and plants. Any new arrivals should be added to a separate holding tank and monitored for symptoms of disease over what we call a “quarantine period”. Although the life span of parasites vary between species, keeping new fish separate for 2-4 weeks is a good length of time to reduce the risk of infection in your main system.

In cases of ich, the parasite has a much shorter life cycle in comparison to other parasite species, and this can be further increased with higher water temperatures. In-fact, raising the temperature of your quarantine tank can hasten the full ich life-cycle to as short as 7 days, meaning you can quickly treat the newly emerging infectious parasites before they can attach to the fish again. To give a rough idea of time spans, the ich parasite will complete its life-cycle in approximately 7 days at 75 °FC (24 °), to as long as 8 weeks at 45 °F (7°C). When treating very cold water for ich, treatments would need to be continued for a longer period of time to ensure you are able to treat the correct stage of the parasites life cycle when it’s vulnerable.

If you’re noticing ich on a fish in your main pond system, you can still quarantine the fish in a separate tank but should still be prepared to treat the entire pond due to the high risk of spreading. If the fish only has a small amount of white spots, you may have caught the disease in the very early stages. If the fish has extensive symptoms, physical and behavioural, treating your entire fish stock is recommended as the parasite has likely already began spreading.

malachite green and formalin to treat ich white spot disease2) Treat Ich using Malachite Green and Formalin

When?  At signs of Ich outbreaks. Can be used on entire pond or within quarantine environment. Treatment frequency dependent on water temperature.

In the past, Ich parasites could often be treated with good hygiene and a solid quarantine routine, but in modern times the disease has become particularly aggressive due to its widespread nature across the fish keeping hobby. For this reason, we now recommend treatment with a wide-spectrum parasite killer at first signs of ich, as the disease becomes more difficult to treat in the later stages of infection. As well as this, the longer the ich parasite is active in the fish, the more chance it has of also developing further complications, such as bacterial and viral infections. Such complications will increase the mortality rate and makes things harder to treat effectively, as the fish will likely be in a much weaker state.

If you notice signs of ich, either when quarantining new fish or in your main stock, you should begin treatment with wide-range parasite killer Malachite Green and Formalin, with our recommended product being Kordon’s Pond Rid-Ich+. Both goldfish and koi should be able to safely tolerate this product when instructions are followed, with it having little negative effect on bio-filtration when diluted accurately. Note: Salt should NOT be used when treating with Malachite Green and Formalin, as it will interfere with the compound and cause burns to the gills of fish.

For best results, a 25% water change should be carried out before each treatment is added to the pond. We would recommend using a pond vacuum to remove water directly from the pond floor, as this will also remove a large amount of parasites in their infectious stage. The frequency of treatment will be determined by your ponds water temperature, which influences the lifecycle of the ich parasite. Temperature can be measured using a basic water thermometer.

To provide a rough estimate of treatment frequency in comparison with temperature, we have created a table below which shows the time between treatments to match the parasites’ vulnerable theront and tomite stages. Although many products state a 24 hour frequency is optimal, this can be overkill in colder water where the parasite is not always in a treatable state.

Water Temperature Treatment Frequency
75°F (24°C)

65°F (18°C)

55°F (13°C)

45°F (7°C)

Treat every day

Treat every other day

Skip 2 days between treatments

Skip 3 days between treatments

3) Prevent External Infections with Melafix

When?  After treatment with Malachite Green and Formalin when symptoms of ich have subsided to prevent lesions becoming infected. 

Due to the external nature of the ich parasite and how it reproduces, the white spots it leaves behind can become a breeding ground for bacteria, especially if the fish is already weak and stressed. In early stages of ich when the parasite is treated at first symptoms, further infections should not be a problem as the koi are still probably healthy. However, with more advanced cases of ich, the lower immune activity and sheer number of lesions across the body greatly increases the chance of infections occurring.

To be on the safe side, if you have had a particularly nasty ich outbreak or your fish are showing signs of external irritation (redness), treating with an external anti-bacterial product can help prevent infection and improve recovery. We recommend Melafix for this, which contains natural tea-tree extract as the main bactericide ingredient. After treating with Malachite Green and when symptoms (white spots) have subsided, you can treat the pond or quarantine tank with Melafix during the recovery period. As well as working as an effective bacteria killer, Melafix will also work against external fungus, fin rot, tail rot, and even cloudy eye.

water vacuums help keep water clean and prevent ich4) Clean the Pond Floor with a Water Vacuum 

When? As part of your cleaning routine to reduce parasites and waste, or during an ich outbreak to remove infectious stage parasites from the pond.

Although small amounts of sludge can be good for pond plants and beneficial bacteria, when debris levels get too high they can become a breeding ground for parasites. Many koi keepers perform a deep clean before winter hibernation sets in to ensure water quality remains good throughout the season and there is less a risk of parasite outbreaks. In the case of ich, pond floor cleaning can be even more effective as the parasite needs to leave the fish and settle in the pond to move onto its more infectious life-cycle phase. Most of the ich parasites will end up directly on the pond liner, which makes fish easy targets as they swim overhead. Even if you have very little in the way of sludge, cleaning the bottom of the pond during an ich outbreak will greatly reduce the number of infectious parasites – shortening the overall treatment process.

Since parasites are too small to be caught with a pond net, the best method to clean the pond and remove them would be with a high quality vacuum cleaner. Vacuums are a rapid method of removing large amounts of sludge, and often come with a variety of attachments for cleaning the floor, edges, and all the nooks and crannies. They can also be used to drain pond water during water changes (useful when treating ich), as the discharge outlet can be positioned into your garden or a sewer drain. Even though they can be expensive, we would highly recommend one if you keep a large number of koi, have sludge problems, or if your pond is prone to parasite outbreaks.

a well aerated pond helps fish with respiratory issues5) Provide Extra Aeration During Ich Outbreaks

When? At first signs of ich to ensure koi have plenty of dissolved oxygen in case of respiratory complications.

As well as infections, another serious complication that can occur with ich are respiratory problems. The ich parasite is not picky with what part of the body it infects, and will just as readily attach itself to the gills as it does the outer scales. Although infection of the gills is rarer during a low-scale outbreak, it can become a serious problem if you have a large amount of parasites searching for new surfaces to attach themselves. Parasites which infect the gill tissue cause damage and inflammation, which reduces the quality of oxygen exchange into the blood of the fish. If you also have low aerated conditions, this can literally be a death sentence to koi and goldfish!

To be safe, you should take steps during signs of ich to install (or turn on) an aeration system to add oxygen directly to the pond water. Although this will not cure the parasite, it will help make sure fish have a surplus of oxygen available in case of gill damage. Extra oxygen will also work to lower overall stress, which in turn will ensure their immune system remains stronger during recovery.  The easiest way to aerate a heavy stocked koi pond is with a dedicated air pump, and we would recommend the Airmax KoiAir range for most sizes of ponds.

9 thoughts on “Koi Ich Treatment Guide (Fish Safe Methods)”

    • Hi Tess,

      Honestly, not much! UV clarifiers should not interfere with prazi treatments, but chemical filtration (e.g., activated carbon) can reduce its effectiveness if you have any present in your system. If it’s just the UV light, you should have no problems with using prazi.

  1. Thanks for the article. Can I take a bubbler from a quarantine pond with 6 ICH infected fish and place it back in my large pond after sun drying it and not infect my fish? Also, can it spread via frogs? Thank you!

  2. Hi,

    I rescued a few goldfish out of a pond on a property that was burned out by the No CA fires. The pond had a lot of algae and was overpopulated by goldfish. What type of treatment and quarentine would you recommend so they can be put into a pond with other fish?

    • Hi Theresa,

      I’m so glad you were able to rescue the goldfish! Are they displaying any sort of health concerns, like strange spots, odd swimming patterns, red scales, fungal growth, etc.? If not, you should be fine to just quarantine them for 2-3 days while observing to make sure none of these things develop. Otherwise, we’re happy to give more specific advice pending your response!


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