How To Cure Fungus on Your Fish

If your fish has a white- or gray-colored growth on its mouth or body (often with a fluffy texture like cotton), it could have a fungal infection. Fungal outbreaks are often caused by stressful or poor water quality conditions and can rapidly lead to secondary diseases, so it’s important to address the problem immediately. In this article, we cover several options for treating fungus, as well as how to stop it from coming back.

When you see any symptoms of illness, the first thing we always recommend is a thorough cleaning of the aquarium. We want to make sure the fish’s environment is optimal and free of any stress factors before we start treatment. Scrub the glass so that you can easily see the fish’s condition, clean out the detritus in your filter, and use a siphon to vacuum the substrate and change the water.

Fungus is often preventable, so the next step is to find the cause of the infection. There’s no point in treating the fish if we don’t stop the source of the problem because then the fungus may come back again in full force.

What Causes Fungus in Fish?

Poor water conditions are a common cause of fungal infections. We see many betta fish with this disease because they’re often kept in tiny containers with no heater or filter. Bettas enjoy temperatures around 78 to 80°F, which means they need a heater if your room temperature is below this range. Also, it helps to house them in an aquarium that holds at least 5 gallons or more to prevent their waste from quickly fouling the water. Doing regular partial water changes and adding live plants (especially floating plants) to a fish tank helps to remove toxic waste compounds before they affect your betta’s health.

Nutrient deficiencies can be another reason why fish get fungus. Fish, like people, need a well-rounded diet to be healthy enough to fight off diseases. Feeding fish from the same jar of flakes all the time is like feeding a person only hamburgers every day. Sure, they can survive, but their bodies probably aren’t in tip top condition. Therefore, make sure to a) provide a wide assortment of foods so that they get all their essential nutrients and b) give them fresh, high-quality foods. Yes, the expiration date on the container may say the food is good for another three years, but every time you open the container, more air and moisture get inside, causing the food to become stale in a matter of months. If you don’t have enough fish to finish the jar in a short amount of time, consider splitting up the food into smaller bags and freezing them to preserve their freshness until you’re ready to use them. Finally, avoid using wet fingers to get food out of the container because this causes the food to become moldy, which can result in fungus or other diseases.

Fish foods

Feed your fish a variety of high-quality foods to make sure they get all the vital nutrients to boost their immune systems.

Many livebearers like fancy guppies and mollies often get fungal infections soon after bringing them home from the pet store. We have a whole article that dives into why livebearers in the aquarium industry are no longer as hardy, but essentially these fish are mass-bred in countries where fresh water is expensive to come by. Therefore, it’s cheaper to raise them in a mix of fresh water and salt water. When your guppies have been raised in brackish water for their entire lives and then suddenly get dropped into a purely freshwater environment, they’re often left in a very weakened state that makes them susceptible to foreign pathogens like fungus spores.

Bottom line: aim to eliminate as many stress sources as possible. Minimize bullying and food aggression among African cichlids. Vacuum the gravel more frequently for bottom dwellers, and keep the water quality high for sensitive species. Avoid keeping shy fish around loud TVs, bright lights that create moving shadows, or high traffic areas in your home. Consider moving older animals that have weaker immune systems into a “retirement tank” with less activity and competition.

How Do You Get Rid of Fungus on Fish?

If your fish’s mouth shows signs of fungus or rot, we recommend using Maracyn. Certain bacterial infections (such as columnaris) look like cottony growths or grayish-white patches around the mouth and thus should be treated with an antibiotic. Before treatment, clean the aquarium and remove any chemical filtration (like activated carbon or Purigen resin). Follow the instructions listed by the manufacturer by dosing 1 packet per 10 gallons of water and repeating every 24 hours for 5 days. Make sure to complete the full 5-day treatment of medication, even if the symptoms seem to disappear, because the infection could still be present in the fish’s system.

If the fungus is located elsewhere on the fish’s body, use a combination of Maracyn and Ich-X. Ich-X contains formaldehyde, methanol, and malachite green chloride, which are effective against fungal infections. Before treatment, clean the aquarium and remove any chemical filtration. If the fungal infection is minor, dose 1 packet of Maracyn and 1 tsp of Ich-X per 10 gallons of water at the same time. Let it soak for one full week, and make sure the symptoms completely disappear. If the symptoms still remain or if the fungal infection is severe to begin with, use 1 packet of Maracyn and 1 tsp of Ich-X per 10 gallons of water, and repeat the dose every 24 hours for 5 days in a row.

If you don’t have a planted aquarium or you’re able to move your fish into a quarantine tank with only fake decor, salt is a great way to treat both mouth and body fungus. You can use any form of regular salt made of sodium chloride (NaCl), but for the purposes of this article, we’re using aquarium salt or rock salt – not table salt, marine salt, or Epsom salt.

After many years of using salt for medicinal purposes, we have found that most tetras, barbs, danios, African cichlids, livebearers, betta fish, goldfish, shrimp, and even plecos are tolerant of salt. However, other fish like anchor catfish are very sensitive to it and should never be exposed to salt. To make sure your fish can endure the salt treatment, start with a low concentration of 1 tablespoon of salt per 3 gallons of water. If the fish is healed after one week, gradually remove the salt via a series of weekly 30% water changes. If the fungus is still active, you’ll need to increase the salt concentration. For detailed instructions on how to do this, please continue reading our full article on salt dosing. You can also use salt in conjunction with Ich-X to pack a powerful one-two punch against the fungus.

Will Other Fungal Medications Work?

In our experience, herbal remedies are not very effective against fungal infections. Once the disease takes hold of a fish, they need stronger medications for a better chance of saving their lives. After many years of running a fish store and helping hundreds of customers, Maracyn, Ich-X, and salt are the treatments we have found that work best against fish fungus.

Ultimately, fungal spores are always present in our aquariums, but full-blown infections are usually preventable. The key is to boost your fish’s health and give them the clean, stress-free environment and necessary nutrients they need to fight it off.

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