Articles > General Guides > White Spot / Freshwater Ich - Cure and Prevention - Ichthyophthirius multifiliis
White Spot / Freshwater Ich - Cure and Prevention - Ichthyophthirius multifiliis
Published by EagleC on 22/04/2010 (116706 reads)

White spot or Ich is a common problem in new setups or from those who have recently added fish. This highly contagious parasite (scientific name Ichthyophthirius multifiliis) can affect virtually any species of freshwater fish but is easy to treat and avoid. This short article describes the prevention and cure of white spot.

White Spot Photos

 “Know your enemy” – The Art of War, Sun Tzu

In order to fight this parasite it’s important to understand its lifecycle.

Trophont Phase

This is the phase that leaves the most visual symptoms. Adult burrows into fish leaving a white crust covering the wound. This is the visual white spot that gives the disease its name. While embedded beneath the skin surface the parasite is protected from water-borne medications.

Tomont Phase

The Trophont drops off the fish and falls to the bottom of the tank or pond leaving a tiny open wound which puts the fish at risk to secondary infection. Complications can include fungus and septicaemia.
The Trophont then rounds up to form the reproductive Tomont (cyst) stage and is also immune to medication thanks to its protective case. Each Tomont undergoes a series of divisions culminating in the creation of between 250 and 2000 Theronts. 

Theront Phase

The Tomont bursts open and the Theronts are released into the water. These swim freely in search of a fish host, once there they will burrow in and the cycle begins again. The Theronts do not feed hence can only survive around 2 days if they do not find a fish host. During this period they are vulnerable to medication.

The entire lifecycle takes from 3 to 28 days or more (parasite can probably overwinter on fish in ponds) depending on water temperature and specific strain of Ich. At 21C (70F) the lifecycle typically takes up to 18 days. At 29C (85F) it takes around 6 days. In most tropical tanks up to 10-12 days is normal. To ensure that you catch every parasite during its vulnerable stage you need to treat for the entire lifecycle.



Prevention is always better than a cure, first you should never buy a fish that has signs of disease or is sharing water with any other fish that looks like it is sick or injured. Symptoms of ich and similar ailments include small white-grey spots on skin and /or fins, each visible to naked eye and up to 1.5 mm diameter, fin flicking and flashing.  Frustrating as it can be to walk away from purchasing a healthy looking fish just because his tank mate has a little fin rot, heeding these warning signs will save you much money, frustration and heartache in the long run. This I tell you from bitter experience.
You can reserve your fish for a week at any half decent store and on returning a week later you can see if the fish and its environment/companions meet your inspection. Do not feel obliged to purchase if there is anything that concerns you.
When you do purchase a fish bear in mind that fish store filter systems are designed to subdue the symptoms of illness, not cure. They get thousands of fish through their tanks every week, many are wild caught and virtually none are adequately quarantined. So all new fish should be considered diseased until proven healthy and quarantined for at least two weeks, preferably four weeks.



There are many medications and treatments available for Ich. The treatment has to be selected based on the individual circumstances. The fish and to some degree the severity of the infection will determine the right actions to take.

General Rules

Due to the nature of Ich, by the time you have identified the disease all the fish in the tank will have been exposed and they will all need to be treated. In a community tank it may be necessary to quarantine a selection of the fish for an alternative treatment regime to the rest.  But you must treat the whole aquarium and all its inhabitants, even if some get an alternative treatment away from the affected aquarium.
It is always a good idea to increase the aeration of the tank during treatment as high oxygen levels will increase a fish’s general state of health and assist its recovery (given ich also damages the gills) but also most treatments will cause the water’s ability to hold or absorb oxygen to diminish. When using medications, carbon should be removed from your filter and you should obviously read and follow the instructions carefully.
If you have invertebrates with your fish check that they will survive the treatment you have chosen without harm. (never expose inverts to copper-based remedies).  If they will not then they should be separated from all the fish before treatment and kept in isolation for at least 4 weeks. This means either quarantining the fish or the invertebrates. If you choose to treat the fish in quarantine you must treat all the fish and leave the display tank fish free for 4 weeks in order to ensure the white spot completes its life cycle and dies.  For a tropical aquarium 2 weeks fish-free should be enough.
Quarantine or Hospital tanks need not be complicated or expensive and are explained fully in another article.


Often a seasoned keeper or fish store adviser will suggest the use of salt to cure a white spot infestation. It is perceived that salt is not a medication and thus safer for the fish and that the parasite cannot survive in salted water.
While there is some truth in this there are also a few problems. Salt is not medication but  a chemical that is alien to freshwater fish and the addition of salt in sufficient quantities to be terminal to this parasite will also be harmful to a wide range of fish. Fish like Cory catfish are sensitive to salt and would almost certainly die if you tried to treat white spot with salt in their tank.
The second problem is in its effectiveness. For years salt has been used as a cheap cure-all in the aquarium trade and it would seem many strains of Ich are now salt tolerant, salt is now one of the least effective ways to kill white spot.
The last big problem is how salt alters the chemistry of the water. Salt water cannot carry as much oxygen as freshwater.
Minor problems include corrosion of certain equipment such as steel impeller shafts, it can kill live plants, damage the filter bacteria balance and it can be hard to completely remove from the tank.
However under some situations salt is the right treatment, for example the clown loach is generally tolerant of salt, high temperatures and relatively low oxygen levels but not of organic dye medications so salt and heat can be used
If you decide to dose with salt you should use sea salt or aquarium tonic salt at a dose of roughly 2 grams salt per litre, for 10 days.
Add the required salt to a bucket of dechlorinated water and ensure it is fully dissolved before pouring slowly into the tank. Bring the water up to the target salinity over the course of a couple of days with multiple water changes. At the end of the course multiple partial water changes will be needed to remove the salt.


While each strain of white spot is slightly different in general at 86F (30C) they begin to lose the ability to reproduce. Unfortunately the ability for water to hold oxygen is also drastically reduced. The elevated temperatures put an extra strain on the fish’s respiratory system, given that gill function may already be impaired due to ich parasites in the gill lamellae. Raised temperatures also speed the white spot life cycle up and the parasite multiplies quicker and quicker until it gets to that critical 86F. This means that a temperature hike can work in the parasites favour and you have to get the temperature high enough to damage the parasite without killing the fish.
It’s also worth noting that increased temperature can kill live plants and while this is of minor importance a dying plant can release nutrients back into the water complicating your white spot issue with a water quality issue.
Generally using temperature on its own is not recommended but increasing the temperature of a cold water tank to 20-24C while medicating can accelerate the parasite lifecycle assisting the medication to work in a single 10 day treatment rather than having to run two or three treatments back to back.
It is vital that if you use temperature in your white spot treatment you significantly increase oxygenation and circulation. Low oxygen levels will not only harm your fish but also your filters balance of friendly bacteria.


There are various organic dye based medications commercially available all over the world that are effective at destroying white spot while not killing filter bacteria or harming the vast majority of fish.
My personal recommendations at the moment would be for Protozin or Esha Exit although most medications are good enough. Be sure to ask independent sources (like on the fk forums) for people’s experiences and view of what is working best. The best medication for white spot is not always the same from one year to the next as new Ich variants with different resiliencies appear.
Like human medicines any treatments should indicate the active ingredients on the package or instructions if they are to be trusted.
If you do not have fish that are considered sensitive to medication then using a proper commercial anti white spot medication is the best option for you. Always follow the instructions and complete the full course, even if all fish become spot-free early on. This is very important.

Ultraviolet Sterilizer

UV sterilizers are highly recommended for those that can’t use medications. While more for prevention than cure some keepers do claim to have resolved minor white spot outbreaks with the early application of oversized UV systems. The UV sterilizer will damage parasites that pass through it either killing them outright or hopefully damaging them enough that they are no longer a threat. Always oversize your UV unit and remember while it will be unlikely to cure a full blown white spot outbreak and is not an alternative to quarantine it will assist in the treatment and could prevent a variety of infections and even subdue the parasites to the point that they are not a health risk to the fish. Certain medications break down when exposed to UV light and in the instructions there will be a note that you should unplug your UV while dosing these medications.

Water Changes

While water changes cannot cure white spot you can use them to reduce the number of free swimming theronts. By vacuuming the gravel you can also reduce the tomonts which will reduce the rate of infection. Both temperature and salt treatment should be combined with daily water changes of around 25% and gravel siphoning.  
If you need to perform water changes when treating with medications you must medicate the replacement water appropriately so as not to dilute the effectiveness of your treatments.



You should always wash your hands directly before and after putting them in a fish tank. This helps prevent you introducing infection to the tank and is also for your own safety. Humans cannot catch ich but like all animals some diseases fish live with can be harmful to humans. This is especially important during a disease outbreak and if you have multiple tanks you should wash hands and arms between working on each tank to avoid spreading diseases from one tank to another. Make sure you rinse well, soap is also very harmful!

If you have more than one tank it is important that nothing is moved from one tank to the other without first sterilising completely. In most cases simply avoid using the equipment from an infected tank. To sterilise equipment for the purposes of Ich either soak in boiling water or leave it to completely dry out for several days. Please note that boiling water can damage certain rubbers and plastics.



Hopefully I’ve been able to show you that white spot is a completely curable and more importantly a preventable and in many cases an avoidable disease. Keep your eyes open and your wits about you and best of luck.

There are always going to be situations that the articles can’t assist you with so please make good use of the forums. They are there so that experienced enthusiasts and new keepers alike can get support and share knowledge.

Author: EagleC
With thanks to Dr Peter Burgess at Mars Fishcare

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