What is Fish Fungus and How to treat it?

fish fungus in fish tank

Fungal infection (Fish Fungus) is one of the most common diseases found in tropical fishes. These are more common in fishes suffering from injury or trauma. Fungal spores are the main reason behind this disease, which can be found in almost all fish aquariums. 

Poor water quality increases the risk of fungal infection. It is easy to identify fungal infections. These infections have a white and fluffy appearance. As this infection worsens, it can become gray and then red in appearance. In this article, we will deal with what is a fish fungus and how to treat it.

Fortunately, these infections are associated with only the external tissues of the fish and its eggs. Some infections are because of pre-existing trauma or stress. It can also occur due to some pre-existing injury. Generally, a two-part treatment is used to cure fish fungus effectively.

Some fungal infections can infect the internal organs of the fish, and they can be very harmful. We will discuss them in this post in a while.

Some common fungal diseases in fish

Here are some of the most common fish fungus diseases.

Cotton Wool Disease

The cotton wool disease is a common name for a variety of fungal infections that affect the external tissues of the fish. It is limited to fins, skin, and mouth. This infection has a characteristic fluffy appearance. Infection can be found in areas where the fish has undergone previous disease or injury. The two most common types of fungi that can cause this infection are Achyla and Saprolegnia. Other fungi may also be responsible for this infection, and there may be more than one type of fungi at the same infected spot.

Tropical fish fungus treatment includes the use of fish fungus treatment salt. You can use Freshwater Aquarium Salt or any other aquarium salt available in the market. Many times the entire tank has to be treated. However, if the infection is limited to only a few fishes, then individual treatment in a separate tank is the best option.

Egg Fungus

If the fish in your aquarium are breeding actively, then their eggs may be surrounded by a fluffy white infection. In this case, also most of the nuance is caused by the Saprolegnia and Achyla class of fungi. These fungi are already present in most aquariums and can infect infertile, damaged, or diseased eggs. The problem escalates when this infection spreads to healthy eggs, which is a common situation when eggs are left in an abandoned aquarium. 

Once these fungi infect the egg, there is no effective treatment. You cannot treat the infected eggs. However, you can stop it from spreading to other healthy eggs. You must be careful between a healthy opaque egg and a fungi infected egg. You can use liquids like Methylene Blue to control fish fungus. 

Gill Rot

Gill rot is a rare freshwater fish fungus. However, if untreated, it can be deadly for the fish. In this case, the fish has to gasp for oxygen. The gills of the fish are covered with mucus. The main culprit behind this infection is a fungus named Branchiomyces. Unfortunately, if you do not use some good fish fungus medicine, then the fungus can rot the entire gill of the fish.

This infection is common in stressed fish. A high level of nitrates and ammonia in the aquarium further increases the risk of fish fungus. Unfortunately, the treatment of this infection is challenging and often unsuccessful. There have been instances when the fish was cured of this infection using phenoxyethanol baths for the long-term. Increasing the oxygen level in the aquarium may also be helpful. However, the prevention of this disease is more important than its cure.

Fish Mouth Fungus

Fish Mouth Fungus is another type of fish fungus caused by fungi named Flavobacterium. This fungus is more common in new fish. In the initial stages of the infection, you can observe a fungal growth around the mouth of the fish. It can also extend to fins and body. This infection is marked by off-white collaboration and, if unchecked, can completely rot the mouth of the fish.

Other signs of this fungal infection include red ulcers on the surface of the skin and frayed fins. Flvobacteium can also lead to fin rotting. This infection can agitate the fish a lot, and with time they start to “shimmy” (lose control of nerves and muscles). Due to shimmy, infected fish try to avoid eating food. As a result, fish become thin and emaciated. 

Systemic Fungal Infections

Systemic fungal infection is a very rare aquarium fish fungus. Similar to gill rot, this fungus infection is difficult to treat. Unfortunately, there has not been enough research on this disease, so there is minimal knowledge in this field. Lcthyophonus is the primary fungi responsible for this disease. Fish infected from this fungi has poor health. Only a post-mortem diagnosis is possible. Fish suffering from stress and trauma in a poor aquarium environment are more vulnerable to this disease. API PIMAFIX baths are considered successful in curing this disease. 

It is essential to point out that many traditional fungus diseases like mouth fungus and tail rot are not fungus disease at all. They are bacterial infections.

Identifying a Fungal Infection

Look for discoloration on the surface of the fish 

Fungal infection generally shows up on the surface of your fish. Look for any discoloration on the surface of the fish’s skin. It will look something like white-fluffy discoloration.  

Your fish will generally develop white patches or white film on its skin surface. It looks like some general discoloration, but a closer look reveals whitish fungus-like growth.

Notice problem in fish eyes

Fish Eye fungus (Popeye) is also a common fungal infection. In this case, the eye of the fish is enlarged. It may seem non-functional and a little upward positioned. The color of the eyes also changes to filmy-white. If any of these symptoms are observed, treat it soon to eliminate the chances of other fungal infections. 

Look for a change in the behavior of the fish

 If your fish is suffering from fungal infection, it will show some changes in behavior. Not only that, but the other fishes may also behave awkwardly. If your fish is suffering from severe fungal infection, then it would lie in the bottom of the aquarium. They may even gasp for air at the top of the water. They will avoid mixing and playing with other fish. It can also stop eating food if it is very ill.

If you check your fish daily, it is easy to observe any change in behavior. If you understand your fish and know how it behaves, acts, and plays, you can easily spot fish fungus.

Effective Fish Fungus Cure

The most common infection in a fish is a fish fungus. It could be caused due to fungi like Achyla and Saprolegnia. It can lead to illness and weaken the immune system of the fish. Moreover, these fungi are contagious and can be fatal if not properly treated. So it is essential to use some effective fish fungus medicine. Let us find out some effective fish fungus treatments.

pop eye in fish

Treating Your Fish

Set up the treatment tank

These infections are contagious, so it is crucial to separate the infected fish from all other healthy fishes. You can use a small tank for this purpose. It should be big enough so that your fish can move around in it. Add some water to it and bring its temperature to around 21 – 25 C. You can use an aquarium heater for this purpose. Eliminate all unnecessary chlorine from the water. Make sure it has the correct PH balance.

This treatment tank doesn’t have to be very big. It can be between 10 – 20 gallons. The tank is enough to give your fish enough room to move around. Your fish will be there for the treatment process only, which can last for a few weeks. Once your fish is treated, it can be put back into the permanent tank. 

Separate the infected fish from the permanent tank

Take your infected fish out from the permanent tank. The infected fish from all the other healthy fishes. These fish fungi are extremely contagious, separate the infected fish as soon as possible.

In case all the fish in your aquarium are infected, even then, you should treat them in a separate aquarium. This process will allow you to clean the permanent tank while treating the infected fish. Most often, these infections are because of poor quality of water.

Add some fungal treatment into the water

To cure fish fungus, you can buy a fungal treatment from any local store or online retailers. It can be a tablet or a liquid that should be administered very carefully. You should read the package very carefully. Follow all the dos and don’ts given in the guide. You will have to add medicine to the treatment tank. After this, you will have to transfer your fish into the tank for a few weeks.

The most commonly used fish fungus medicines are potassium permanganate, malachite green, povidone-iodine solution, and formalin.

This treatment is most widely used when treating a fungal infection in the outside of the fish body. This method is easy and effective. You should take care that holistic medicines are not very successful in treating fungal infections. It would be better if you could use strong antibiotics. 

Give your infected fish a salt bath 

Along with medications, you can also use a salt bath for fish fungus treatment. The recommended concentration of salt should be one tablespoon per gallon of water in the tank. You should add this salt in the treatment tank and not in the permanent tank. Mix the salt properly till it completely dissolves. You should leave your fish in this condition for 15 to 20 minutes. Next, remove the fish from the water and put it in clean and de-chlorinated water.

You should take care that some fish like tetras cannot tolerate salt baths. On the other hand, fish like goldfish can tolerate it very well. It is essential to know if your pet fish can tolerate salt baths or not.

You can continue to salt bath your fish even after a few weeks of treatment. This step will ensure that the infection is completely cured.

Clean your treatment tank regularly 

The most common cause of fungal infection is the bad quality of water in the aquarium, which is where most of the fungi dwell. During the treatment process, it is vital to maintain a sterile and clean environment. It is essential to keep your temporary tank clean. So how do you clean your tank? You can scrub the sides of the tank. You can even change twenty percent of the water in the tank for fresh, clean water every alternate day. A clean and healthy environment is vital for the well being of the fish.

Once the infection is treated, put your fish back in the permanent tank 

Once the white fungus on fish is completely removed, you can put back your fish in the permanent tank. You should take care to put the fish back only when it is completely cured of the infection. You can ascertain this if its discoloration is completely removed. If it is eating, swimming, and acting normally, it is also a sign that fungus infection is cured. You should leave the fish in the temporary tank for one more week, even after fungus infection is treated. This method will help it to recover all its health before joining its fellow mates. 

When you put your fish in the permanent aquarium, observe if the other fish show signs of aggression. Try to watch out for fungal growth in healthy fish. If the infected fish, as well as the healthy fish, behave normally, we can conclude that the fish is cured.

Preventive Measures for fish fungus

There is a famous proverb “Prevention is better than cure.” Let us find out some preventive measures that can be taken to eliminate the chances of your fish being infected by fungi.

Regularly change your feeding schedule 

One of the most common reasons behind fungal infection is too much organic matter in the tank. You can take measures to clean your tank of these organic wastes and change the time when you feed your fish. You should feed your fish only as much as it can eat. If you put more food in the tank, it will be a waste of food as well as it will make the water dirty. 

You can give small portions of food to your fish. Try to feed your fish several times a day. It is better to feed your fish 3 – 4 times a day in small amounts instead of two large meals. You can decide how much food it needs based on size, age, and species of the fish.

Once you have identified the amount of food, your fish needs do not change it. Not following a proper feeding procedure can stress out the fish and escalate the chances of fungus infection. 

Regularly clean your fish tank 

You should clean your tank at least once a month. Take out your fish and put it in a separate tank. Clean the permanent tank thoroughly from top to bottom. You should remove half of the water in the tank and set it aside. Put back the water into the tank after cleaning. Properly clean all the plants, gravels, and toys. You can use a sponge to clean the corners and sides of the tank. Finally, put back all the toys and plants into the tank. Pour the reserved water and use clean water to fill the tank.

Fix the temperature of the tank and then put your fish into it. Do not put the fish first and then change the temperature, which can be fatal for the fish. Cleaning your tank once a month will remove other organic matters, excess foods, and feces and stop fungal growth.

Regularly check your fish for any fungal growth and related health problem 

Most fungal infection occurs because the fish is already suffering from some health issue. If you can find out about the health issue of the fish, then its immune system can be improved to fight the fungal infection. It is better to prevent fungal infection instead of curing it.

Most often, fungal infection occurs at the same site where the fish suffered the previous injury. Once the skin surface is broken or injured, the fungi can immediately attack that spot. The fish fungus is usually caused because of parasitic infection, injury, or bacterial infection.

You should treat any disease your fish is suffering. The sooner you treat the disease, the better it is for the fish. Once its immune system is compromised, it will not be able to fight the fungi. For example, if your fish is suffering from parasites, you must provide it with medicated food to cure the infection. 

Some effective fish fungus medication

Treating fungal infection in your fish is extremely important, as it can lead to severe consequences. Some fungal infections can even lead to death. They are highly contagious and can affect other healthy fish as well. Here are some effective medications that can be used to treat these conditions.


We can use this medication to treat mouth rot, fin rot as well as cotton wool fungus. This medication can be used in salt water as well as tropical freshwater aquariums. You should not use this medication in aquariums containing Mormyrids. 

  • Shake the bottle well for about 30 seconds before using it. Remember to remove all the zeolite and carbon filter media out of the aquarium before using it. 
  • 5 ml of this medication is enough to treat 10 gallons (38 liters) of water. Measure the volume of water in the aquarium. Mix the medicine with some water. Stir it till it completely dissolves. Finally, pour this mixture over the surface of the aquarium.
  • Use the dosage daily for 7 days. After 7 days change 25% of the water in the aquarium.

API Aquarium Salt

This medication can increase the immunity of your fish. It can help to maintain a constant salt/ fluid balance in the aquarium, which can be very useful when the fish is suffering from some stress or injury, which can positively impact the overall well being of the fish. We can use it in a variety of ways:

  • As an aquarium tonic
  • To minimize the stress effect on your fish
  • As a PH buffer
  • To reduce the toxicity of nitrites

You can pour this salt directly into your aquarium. Do not use a large quantity of salt as it can take a while to dissolve. Slowly mix the salt in small quantities. Add 1 rounded tablespoon for every 5 gallons (20 liters). Gradually increases the salt content for 3 – 4 days. Do not maintain this salt content for more than two weeks. It can start to damage the plants after two weeks. One can alter the concentration of salt by changing the volume of water.

Kordon Methylene Blue

Use Kordon Methylene Blue to prevent the outbreak of bacterial and fungal infections in your aquarium. It can also prevent parasitic infections. 

There are times when your fish is stressed out. These may be during cleaning the tank while adding a new fish, poor water quality, or bullying in the fish community. Stress is one of the main reasons behind the fungal infection. Use Kordon Methylene Blue to prevent a fungal outbreak in your aquarium.

Use this medication in saltwater and freshwater aquarium. Fish like mormyrids cannot tolerate this medication.

  • Shake the bottle well before use. Remember to remove all the zeolite and carbon filter media from the aquarium. 
  • 1 teaspoon of this medication is enough to treat 10 gallons of water. 

So this was all about fish fungus, types of fish fungus, and how to treat it.