What Causes ICH on Fish [and How to Treat It]

One of the most common diseases that aquarium fish can get is ICH or ichthyophthiriasis. Although common, this disease can be fatal if left untreated, so it’s important to know what causes ICH on fish and how to treat it.

And this is what we’re going to learn in today’s article: how to treat ICH, what causes it and, the most important part, in my opinion: how to prevent ICH (as this is the best approach for all aquarists).

But, let’s start from the beginning!

What is ICH & how to diagnose it in fish?

fish in aquarium treated from ICH

ICH is caused by a parasite called Ichthyophthirius multifiliis, which can affect both freshwater and saltwater fish.

This parasite can cause several symptoms, including white spots on the fish’s body, lethargy, and loss of appetite. The first one – the white spots on your fish – are the most common symptom and the easiest to notice.

If you notice any of these symptoms in your fish, it’s important to take action immediately.

What Causes ICH on Fish?

I fortunately didn’t have to deal with my fish suffering from ICH too often. Actually, it just happened once, when I introduced one of my now-favorite fish, Microrasbora Galaxy, to one of my small aquariums. (By the way, they are perfect for a jarrarium!)

I am 100% sure that in the case of my Microrasbora, the main cause was stress. They developed the ICH symptoms a couple of days after I have acquired them but fortunately they ALL survived.

More on that later, but for now let’s check out what causes ICH on fish.

Poor Water Quality

Poor water quality is one of the main causes of ICH on fish – I would go as far as saying that it is the main cause in general, and for multiple types of diseases in fish or other problems, including white spots on your aquarium’s glass or algae build-up (but the latter is, at least, generally harmless to fish).

Back to ICH, if the water in your fish tank is not clean, it can create the perfect environment for parasites like Ichthyophthirius multifiliis to thrive in.

Poor water quality will also weaken your the immune system of your fish, making them more susceptible to all types of diseases, including ICH.


Stress can also cause ICH on fish. As I said, I believe that the only time some of my fish experienced ICH was because of stress.

Fish can become stressed due to a variety of factors, including poor water quality, overcrowding, and changes in their environment.


Overcrowding is another factor that can cause ICH on fish. When there are too many fish in one tank, it can create a stressful environment that weakens the fish’s immune system. This can make it easier for parasites to infect the fish.

Overcrowding itself is not necessarily a reason why your fish develop ICH, but it is usually the cause behind either a dirty aquarium or improper water conditions or general stress in fish.

Poor Nutrition

Poor nutrition can also weaken a fish’s immune system and we already know that this goes hand in hand with higher chances of them getting ICH.

If you’re not feeding your fish a balanced diet, it can lead to nutritional deficiencies that can compromise their health.

So make sure you always choose the right food for your fish and never over-feed as excess food can ruin the quality of the water in your aquarium.

Speaking of fish food, read my previous article to learn what fish can eat besides fish food.

Introduction of New Fish

Introducing new fish into your tank can also cause ICH. New fish can carry parasites like Ichthyophthirius multifiliis, which can infect your existing fish.

This is why it’s important to quarantine new fish before adding them to your tank to prevent the spread of diseases. Keep the fish quarantined for up to 2 weeks to make sure they’re healthy – you don’t want to risk having them get all your fish sick, right?

How to Treat ICH on Fish?

If you notice any symptoms of ICH on your fish, it’s important to take action immediately.

Here are the steps you should take to treat ICH on fish – but have in mind that usually, this is a very serious disease for fish and there might be casualties.

Increase Water Temperature

One of the most effective ways to treat ICH on fish is to increase the water temperature in your tank to destroy the parasite.

Ichthyophthirius multifiliis thrives in cooler water, so raising the temperature can help to kill it off.

However, it’s important to raise the temperature gradually to avoid stressing your fish even more.

Also, make sure not to raise it too much – get it to the maximum temperature your fish can survive and keep it like that for at least a few days (you should see the white spots on your fish disappear during this time).

Use Medication

There are several medications available that can help to treat ICH on fish. These medications are typically added to the water in your tank and can help to kill off the parasites.

However, it’s important to follow the instructions carefully and not to overdose the medication, as this can harm your fish. Discuss the best medication to use with your local pet store employees.

Salt Treatment

Salt treatment can also be effective in treating ICH on fish.

Salt helps to create an environment that is inhospitable to parasites like the one causing ICH in fish. I am not a huge fan of this type of treatment, because adding too much salt can harm your fish (if it’s freshwater ones we’re talking about).

If you want to go this route, though, add 1 teaspoon of salt per 2 gallons of water to treat ICH.

The treatment should last for a maximum of 14 days, but if you see no improvement in the condition of your fish after 5 days, add 50% more salt to your aquarium.

I repeat: this is risky in my opinion as you can easily add too much salt, so it’s best to use the other methods recommended above.

Clean Your Tank

Cleaning your tank is also important when treating ICH on fish. Vacuuming the gravel and changing the water can help to remove the parasites from your tank and it should always be done BEFORE starting the treatment and AFTER.

It’s also important to clean any decorations or equipment in your tank to prevent the parasites from re-infecting your fish, but don’t clean the tank and make water changes DURING the treatment (unless you are specifically told to if using medicine, for example).

Can ICH be prevented in fish?

Yes, ICH can generally be prevented by maintaining good water quality, avoiding overcrowding, providing a balanced diet, and quarantining new fish before adding them to your tank.


ICH is a common and often fatal disease that can affect any type of fish, but if you practice good hygiene and take the minimal safety measures like quarantining new fish before adding them to your aquarium, you should be fine.

However, if you notice the ICH symptoms like white spots on your fish, lethargy, and loss of appetite, separate the fish that have these symptoms and start the treatment ASAP.

While ICH can be difficult to treat, there are several effective remedies, like using medications from the pet store and changes in water temperature to battle the disease.

As I said, I went through the hell of seeing my fish get ICH, but fortunately I managed to treat the condition before it was too late. I am sure that you will be able to do the same if you follow my recommendations above.

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