Fish Fungus: What It Is and How to Handle It

Last Updated on 2023-08-08

Aquarists who take good care of their fish tanks will rarely have to treat sick fish, but you can’t be sure that your fish will never get sick. Almost all health issues can be avoided by keeping the water quality in check, giving the fish a variety of high-quality fish food, and making sure they have a good place to live. Knowing how to keep diseases from spreading and how to spot and fix problems before they get out of hand will help you enjoy your aquarium for years. Read on to find out how to maintain your fish healthy, detect problems early, and cure common fish diseases.

What Causes Fish Fungus?

Fungus infections are one of the most common problems that tropical fish get sick from. Since fungal spores are in every fish tank, they can quickly spread and cause problems for fish that are stressed, hurt, or sick. Here are seven reasons why your fish might have fungus.

1. Poor Water Quality

Poor water quality is by far the main reason why fish get fungal diseases. When fish live in a fish tank with a lot of organic matter, not enough oxygen, and a lot of ammonia, their gills and skin are more likely to get hurt. Poor water quality can also weaken a fish’s immune system, making it more likely to get fungus.

2. Nutrient Deficiency

Fungus can also grow on fish when they don’t get enough nutrients. Like people, fish need to eat a variety of foods to stay healthy and fight off diseases. If they didn’t, their immune system would get weaker, which would make them more likely to get sick from fungi.

3. Cold Aquarium Water

Fungus in aquariums is also often caused by water that is too cold. If the water in your aquarium is too cold, your fish’s body systems can slow down a lot, which can make their immune responses weak or slow. These things make it more likely that your fish will get sick because they won’t have the resources they need to fight off fungal infections and other diseases.

4. Rapid Changes in Water Parameters

Water changes that are too rapid are stressful for fish and must be avoided. You must keep the tank’s parameters stable and constant to keep your fish from becoming stressed and to reduce the likelihood of fungal infection. You want to make sure that the parameters of your tank meet the specific needs of the fish you’re keeping.

5. Overstocked Aquarium

There shouldn’t be more than one inch of fish for each gallon in your fish tank. If you contain more fish than this, they won’t be able to breathe because there won’t be enough oxygen-rich water in your aquarium. This will significantly decrease the immune system of all the fish in your tank, thereby increasing their risk of getting bacterial and fungal infections in the future.

6. Poor Oxygenation

Lack of airflow is one of the common reasons why fish tanks get fungal infections. If your tank doesn’t have enough airflow, there won’t be enough oxygen, and harmful gasses like ammonia will build up quickly. This will make your fish constantly stressed, which will make them more likely to get a fungal infection or other diseases in the future.

7. Leftover Fish Food

Moldy fish food that sank down to the bottom of the tank doesn’t directly hurt the health of the animals in your tank, but it will hurt their health in other ways. The problem is that these moldy leftover foods will make the water quality even worse, leading to more bacteria and even the growth of other types of fungi and mold.

Gold fish or goldfish floating swimming underwater in fresh aquarium tank with green plant. marine life.

How To Treat Fish Fungus

Fungi are in every aquarium, but they rarely cause problems as long as the water is clean and the fish are healthy. But there are numerous ways to treat fish infections if your fish ever got sick. Here are six ways to rid your fish of white fungus.

1. Organic Dyes

Fungus can be treated with several patented medicines, usually based on organic dyes like malachite green. These medicines are safe to use on most fish, but they can’t be used in tanks with certain delicate species. Just make sure to move the sick fish to a quarantine tank so it can be treated without spreading the disease to other animals.

2. Use Aquarium Salt 

Salt is highly effective against fish fungus because fungus cannot tolerate it. To treat your fish, mix one tablespoon of non-iodized salt per 3 gallons of water. Remember to isolate any diseased fish in a separate quarantine tank.

3. Tea-Tree Oil

Many aquarists sometimes say that tea-tree oil is a less dangerous antifungal medicine. Tea-tree oil medicine can work up to a certain point, but it doesn’t always work and may not be powerful enough to treat severe fungal infections. Tea tree oil is best thought of as a preventative or safety measure. 

4. Use Interpet Disease Away Treatment

Interpet Treat Disease Away is an aquarium water treatment that fights disease-causing bacteria and fungus in freshwater and tropical fish tanks. The treatment is perfectly safe for use in a tank with fish in it. However, it shouldn’t be used in aquariums with fish that don’t have scales or invertebrates.

5. Install An Aquarium Filter

Filters are a good way to dispose of harmful pathogens and waste in your tank while also giving your fish oxygen to breathe. If the water quality is good, there will be less chance of fish getting fungal infections. When picking a filter for your aquarium, ensure that it has the right filtration, so your aquarium water is always clean.

6. Change The Water

The fish might not get better right away, but changing the water is a good start. By taking out the dirty aquarium water and replacing it with clean, fresh water, you are basically diluting the excess nutrients that can hurt your fish tank’s environment.

How To Treat Fish Fungus With Salt

Sodium chloride is one of the best, all-around “medications” on the market. It can kill bacteria, fungus, as well as external parasites. It has also been tested and proven by many aquarists, so it is safe to say that it can be used in freshwater tanks. Here’s a step-by-step guide on how to use salt to treat your fish with fungi.

1. Prepare A Quarantine Tank

A quarantine aquarium tank is used to help keep diseases from spreading as much as possible. Additionally, you don’t want to add salt to an aquarium filled with plants as it can kill plants. Put the quarantine tank in a different room away from your main display tanks and use separate tools to avoid cross-contamination.

2. Add Aquarium Necessities

Set up the quarantine aquarium by putting in the filter, heater, and any other aquarium accessories needed for treatment. With this, you can regulate the conditions of the water in the quarantine tank. Also, sick fish tend to seek cover, so providing them with more places to do so will make them more at ease.

3. Transfer Infected Fish

Before putting your infected fish in a quarantine aquarium, make sure that the temperature of the water in both aquariums is the same. This will keep your infected fish from being shocked by the temperature. You can just use a pitcher to move fish.

3. Add The Right Dosage Of Salt

Most of the time, it’s enough to add 1 tablespoon of salt per 3 gallons of water to treat bacterial and fungal infections in fish. Some aquarists recommend dissolving the salt in a small glass of water before pouring it into the quarantine tank. Keep in mind that the most salt you can add is 1 tablespoon per gallon; beyond that dosage can worsen your fish’s health.

4. Observe and Wait

Look at how your fish looks and acts to see if it is getting better. You can also help strengthen their immune systems by giving them high-quality food full of nutrients and easy to clean up.

5. Put The Recovered Fish Back

Once the quarantine period is over, and your fish has healed, you can put them back in the main aquarium. Make sure to use only things that have been sterilized when transferring. Also, clean the hospital tank and put everything away in a dry place.

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Best Fish Fungus Treatment

Fish fungus is a common problem in aquariums and can be difficult to treat. Fortunately, there are several treatments available that can help keep your fish healthy and fungus-free. Here are five of the best fish fungus treatments.

1. Aquarium Salt 

Adding salt to an aquarium helps reduce the risk of fungal infections, as it can help reduce the growth of fungi. Aquarium salt is safe for most fish but should be used cautiously if you have sensitive or delicate species.

2. Antifungal Medications

Antifungal medications are available in pet stores and can be used to treat fungal infections in fish. These medications come in liquid form and are usually applied directly to the affected area. Be sure to read and follow the directions carefully, as overdosing can have serious consequences for your fish.

3. Vinegar Solutions

Vinegar can be used to treat mild fungal infections in fish, as it helps lower pH levels in the water and reduces the growth of fungi. To use this method, mix one part vinegar with ten parts water and add it to the aquarium.

4. Copper Sulfate

Copper sulfate is a common treatment for fungal infections in fish. It works by disrupting the cell membrane of fungi, making them unable to grow or reproduce. To use copper sulfate, add one teaspoon per ten gallons of aquarium water.

5. Natural Remedies

There are also natural remedies available that can help prevent and treat fungal infections in aquariums. For example, adding a few drops of lemon juice or garlic oil to the water can help reduce the growth of fungi. Additionally, using chamomile tea bags as filter material can also help inhibit the growth of fungi. 

Why Do Fish Egg Have Fungus?

Fish eggs are very susceptible to fish fungus as they are basically a sac of packed nutrients waiting to be infected. However, the fungus didn’t just appear on top of the fish eggs out of nowhere. Here are six reasons why there is fungus on your fish egg.

1. Poor Water Quality

When the water quality is bad, harmful toxins like ammonia and nitrite can build up. This can make it easier for fungi to grow, which could be why fish eggs have it.

2. Decaying Organic Matter

Fungi spores can be found in almost every aquarium, and it will float around until it lands on something that allows them to grow and spread. Too much decaying organic matter floating around in your fish tank can make it more likely that the eggs will get infected.

3. Poor Water Filtration

Poor water filtration can cause toxins to build up which could also cause the quality of the water to go down, which helps algae and fungi grow. As the quality of the water in your tank goes down, the fish eggs are likely to become infected with fungus.

4. High Levels of Ammonia

Fish egg fertilization and the number of eggs that hatched were more affected by high levels of ammonia. When there is a lot of ammonia in the water, it can cause bad eggs, which can then lead to infections caused by fungi.

5. Unfertilized Fish Eggs

One reason the fish eggs have fungus on them is that they might not have been fertilized. Fungus can easily take over fish eggs that haven’t been fertilized, are broken, or are already dead. Fungus can grow on these eggs, and the fungus can slowly spread to nearby healthy eggs..

Best Fungus Eating Fish

Aquascaping in an aquarium is a lot of work, and fungus can make a mess of it. Luckily, there are ways of getting rid of it. One method for clearing a fish tank of fungus is to introduce some fish known for their voracious appetites for fungi. Below is a list of fish that are known to enjoy a fungus meal.

1. Bristlenose Pleco

The Bristlenose pleco, which is also called the Bristlenose catfish, eats a lot and is a great addition to large aquariums. When fully grown, these fish can reach a length of five inches. These fish live at the bottom of the water and eat any kind of algae. They will also happily eat fungus.

2. Mollies

Mollies are omnivores that eat fish flakes, frozen meals, and even live foods. They can also eat algae and fungus that grows in aquariums. It’s fun to keep these fish in a tropical freshwater tank because they’re easy to care for, and they reproduce quickly.

3. Twig Catfish

The Twig Catfish is yet another kind of Catfish that’s also good at getting rid of aquarium fungus. Twig Catfish can eat many different kinds of algae and fungus, but you must give them algae tablets at least twice or three times a week to keep them healthy.

4. Siamese Algae Eater

Siamese Algae Eaters, as their name suggests, graze on different kinds of algae and fungus. They will eat anything they can find, including tank decorations, viewing glass panels, and even leaves of plants. But these fish can be very territorial, so we suggest big tanks with a lot of aquatic plants to ensure that each Algae Eater can claim its own patch. 

5. Otocinclus Catfish

These fish are very small, and they rarely get bigger than 2 inches. This helps them get into tight spaces and eat hard-to-reach fungus. Although small, these fish are small, they can eat a lot of fungus in such a short period of time.

How To Tell If Fungus Treatment Is Working On Fish

It’s not easy to deal with fish fungus, and it could be hard to find out if the treatment you gave to your fish is working. However, there will be noticeable changes in your fish’s behavior that indicates that the treatment is working. Here are seven signs that the fish are getting better.

1. Fish Is Swimming Effortlessly

If your fish has started swimming gracefully and effortlessly, it is a sign that the treatment is working. Healthy fish will usually swim actively around the tank as it signifies that it is no longer stressed.

2. Fish Is Alert

Know how active your fish are and look for changes in their habits. If they’re no longer lethargic and show signs of alertness, it is usually a good sign that your fish is recovering and the treatment is working.

3. Fins Are Erect

When fish are stressed or sick, they often clamp their fins. This is often the first sign that something is wrong. If the fish’s fins are spread out, and it doesn’t have any gray or white spots, it is healthy and getting better.

4. Good Appetite

A fish in good health has a good appetite. If they don’t refuse food care, it means it’s getting better, and the treatment is working. But be careful; just because your fish is starting to do well doesn’t mean you should give it more food.

5. Bright Red Gills

One way to tell if the treatment worked is to look for gills that are bright red and move in regular patterns. The fish’s gills shouldn’t move too fast like they’re gasping for air, and there shouldn’t be any redness or white or gray spots.

6. Good Body Colouration

A healthy fish should have that healthy glow. The scales should be even and smooth with healthy color and no rough patches. This will indicate that the treatment is working and it is recovering.

7. Clear Eyes

When a fish’s eyes get big and cloudy, it means that it is very stressed. If you no longer see that in your fish, it means that it is getting better.

Is Fungus On Fish Contagious?

There are many kinds of diseases that can spread in an aquarium, but fungal diseases are one of the most common. There are many kinds, and each one will show up in your fish in a different way. Some will only hurt certain kinds of fish, but others can hurt almost all fish.

It’s good news that fish fungi don’t spread to other fish as some diseases and parasites do. Even though fungal infections aren’t usually contagious, they can indeed be caused by many things, such as bad water, too much leftover food, open wounds, and so on. Infected fish must be treated right away with antifungal treatment, preferably in an isolated hospital aquarium.

Even though there are ways to treat it, it is better to avoid it. The water in the aquarium needs to be kept as clean as possible. You shouldn’t take a chance on these fungi growing on fish if you keep fish. 

Will Fish Fungus Go Away By Itself?

Fungus spores take advantage of every chance they get to invade organic matter, even living tissue. When they get into your fish, they will eat all the organic materials, including organs and deeper tissues. If you find fungi in your fish, you should take steps to fix the problem right away.

Fungus won’t go away on its own and needs to be treated right away because it spreads quickly and makes the fish more likely to get other infections, like fin rot. Fungus can even kill a fish if nothing else is done about it. It will stick to your fish and stay there until you treat the fish or until your fish is dead.

Lucky for us, there are many ways to get rid of fish fungus on our own. This includes adding a pinch of salt or using water treatment products to directly kill and get rid of fungus. Just make sure to put the infected fish in a separate tank first, as these treatments can hurt other fish and plants.

How Long Does it Take for Fish Fungus To Go Away?

There is a good chance that the spores of fish fungus can be found in your aquarium. But it won’t sprout up right away because it needs decomposing matter to feed on. If your fish has any cuts or scrapes, the fungus can also grow on it

How long fish fungus stays on your fish depends on how bad the problem was in the first place. If you have treated your sick fish right away, they should be better in 4 to 5 days. Because fish have open wounds, it’s essential to keep the water clean so that a second infection doesn’t happen.

However, it is better and more recommended to prevent fish fungus from happening than curing it. Fish fungi spores are opportunistic and will only grow once your fish is stressed or injured. To prevent this from happening, make sure that your aquarium is not overcrowded and isolate aggressive fish. 


Is API Fungus Cure Safe for Scaleless Fish?

There’s no evidence that API Fungus Cure is safe for scaleless fish. But, according to DailyMed, this product contains a type of malachite green, which is known to be toxic to most fish without scales and other freshwater fish.

Is Epsom Salt Good for Fish Fungus?

The National Park Aquarium says that Epsom salt, a type of mineral salt, is used to make fresh water less hard. It is suggested that aquarium salt be used to treat fungal and bacterial infections.


Fungi are a common aquatic problem in a fish tank, but they can scare even the most seasoned aquarist. It can be caused by a lot of things, like dirty water, a lot of ammonia, or water that is too cold. This fungus can be deadly, but your fish and its fish eggs don’t have to die because of it. There are many ways to get rid of it in fish, such as treating infected fish with salt or organic dyes for aquariums. There are even products for your aquarium that are made to get rid of fungus from your fish. Remember that it is better to keep your fish from getting these infections in the first place than to treat them.

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