Pleco White Fungus Disease – The Causes and Treatments

Alison Page

Alison Page


Pleco White Fungus

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There are around 150 species of plecos, many of which are seen regularly in the hobby.

Plecos or plecostomus are peaceful, bottom-dwelling fish that are generally pretty hardy if kept in clean conditions and offered a high-quality diet.

However, plecos can be vulnerable to a few diseases, one of which is white fungus.

Plecos sometimes develop white fungal growth on their head, body, and tail. So, what causes white fungus in plecos? How can you treat it? And what can you do to prevent the problem from recurring?

Read this guide to learn everything you need to know about identifying, treating, and preventing white fungus in plecos.

What Is White Fungus in Plecos?

The fungus appears on fish as fluffy, cotton-like white or grayish growths, typically on the fish’s body, head, and tail. All species of fish can be affected by fungus, including plecos.

There are two forms of infection that present as white fungus or mold.

Fish Fungus

Fish fungus is caused by water molds called oomycetes. Several species of filamentous water mold can attack your fish, including Saprolegnia, Achlya, and Leptolegnia.

Fish fungus is pretty common in aquarium fish and usually occurs secondary to an injury that leaves scrapes or tears in the fish’s skin.

The fungal mold spores enter the fish’s tissues through that skin rupture and begin to proliferate, ultimately forming those characteristic fluffy white balls.

The condition spreads rapidly and is highly contagious, so you need to treat your pleco quickly before the fungus gets out of control.

Fortunately, you can usually treat fish fungus successfully with an over-the-counter medication that you’ll get in your local pet or fish store.


Columnaris is sometimes referred to as Saddleback disease or Mouth fungus and appears as fuzzy white growths across the fish’s body and around its mouth.

The disease also causes gill necrosis, fin rot, and skin lesions. If left untreated, Columnaris is often fatal.

The condition is caused by the Flavobacterium columnare bacterium rather than mold. However, because the bacterial colonies have a fluffy, cottony appearance, the disease is often blamed on fungus.

A pleco with Columnaris infection will have patches of fluffy, woolly growths around its mouth. The bacterial colonies typically appear gray or off-white, although they can sometimes appear brown.

As the disease progresses, it will spread to the pleco’s gills and the rest of its face. In severe cases, the infection causes reddened areas on the fish’s head and around its mouth.

In addition, infected plecos are inactive and have a poor appetite.

What Causes Pleco White Fungus?

Fish fungus and Columnaris are both caused by the same basic issues, which are largely preventable.

Poor Water Conditions

Most common fish diseases thrive in dirty conditions where there’s a lot of organic waste matter decomposing in the water. So, if you don’t keep your fish tank clean, you can expect problems.

Poor water conditions are often found in beginner tanks simply because newbies to the hobby often aren’t familiar with good husbandry or are too busy to dedicate the time necessary to maintain the tank.


A regular, weekly, or bi-weekly maintenance regimen is essential for all fish tanks. In the case of plecos, you should pay particular attention to weekly maintenance since these are large fish that generate a lot of waste.

Once a week, you need to change around 20% to 25% of the tank water to remove harmful nitrates and keep the environment fresh.

Use an aquarium vacuum to remove decomposing organic waste, including fish poop, dead plant matter, uneaten fish food, and general detritus.

If algae are growing in your tank, use an algae magnet or scraper to remove algae from the aquarium glass.

Once every couple of weeks, you should remove the filter media from your filter system and rinse it in tank water to get rid of sludge. Periodically, the media will need to be changed in line with the manufacturer’s guidelines.

Incorrect Water Parameters

If you keep your pleco in unsuitable water conditions, it’s likely that the fish will become stressed. That can lower the fish’s immune system, leaving it open to attack by diseases, including fish fungus and Columnaris.

Most species of plecos need a water temperature of between 74° and 80° F. The pH should be between 7.0 and 8.0, with a water hardness or alkalinity in the range of 3 and 10 dKH.

Fluctuations in water parameters are extremely stressful for your fish, so you must keep on top of maintenance and remember to carry out regular checks on the water temperature and chemistry.


Use an aquarium water testing kit to test your aquarium water once a week. If the chemistry in your tank is out, take steps to correct it.

We recommend keeping a digital aquarium thermometer in your fish tank so that you can check the temperature each day.

If the water is too cold or too warm, it’s possible that your heater thermostat is malfunctioning and needs replacement or adjustment.


As mentioned above, stress is extremely damaging to fish health. Stressed fish suffer from a weakened immune system, leaving the creature more vulnerable to attack by parasites or common diseases.

In addition, a stressed pleco might stop eating, further weakening the fish’s immune system and potentially leading to malnutrition.

Stress can be caused by a variety of things, including:

  • poor water conditions
  • incorrect water parameters
  • fluctuations in water parameters
  • aggressive tank mates
  • attack by parasites
  • incorrect diet
  • Overcrowded fish tanks

Solving these problems is pretty straightforward.


If your tank is dirty or the water chemistry is incorrect, take action as described above.

Aggressive tank mates should be removed as soon as possible and rehomed or placed in another tank. For example, problems can sometimes occur if you have a group of plecos including more than one male, as male plecos can be quite aggressive toward their own kind.

Cramped fish tanks are a common cause of disease in freshwater fish. So, to keep your fish healthy and thriving, ensure that you don’t have too many fish crowded into one tank.

Some plecos can grow pretty large, so be prepared to upsize your tank as your fish gets bigger.


If your pleco is injured, that can provide an entry point for fungal spores or bacteria, and a secondary infection often results as a complication.


To keep your fish safe, avoid using sharp or jagged decorations in the tank, and remove aggressive tank mates to prevent fighting and nipping

Plecos have hard scales that provide an armored plating across the fish’s head and back. However, the pleco’s underbelly is soft and vulnerable to damage. Use a soft substrate to protect the bottom-dwelling pleco’s underbelly from scrapes.

Poor Diet

Plecos live on the bottom of the aquarium, largely feeding on scraps that drift down from above. That can lead to malnutrition and a weak immune system, leaving the fish vulnerable to diseases.

We recommend feeding your plecos on pleco wafers and other sinking fish foods to ensure that your pets get plenty to eat.

How Do I Treat White Fungus?

Pleco White Fungus Disease

Columnaris and fish fungus require different treatments.

Columnaris is a bacterial disease that should be treated with an antibiotic medication that you’ll get from good fish stores, your vet, or online.

There are lots of fish antibiotic treatments out there, but I’ve found Maracyn to be a reliable drug that works pretty well.

Fritz Aquatics 72 Count Mardel Maracyn
  • Maracyn Two powder is developed for use in aquariums. Due to its unique properties, it is absorbed by the fish through the skin.
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If your plecos are infected with fish fungus, effective treatments include metronidazole, praziquantel, and levamisole. These treatments are especially effective when delivered in food.

Secondary bacterial infections can also be treated successfully with antibiotics such as nitrofurazone or erythromycin.

Before Treatment

Before treatment, we recommend cleaning your tank and removing all chemical filter media, such as activated carbon, as that could remove the fish remedy from the water before it has a chance to kill the disease.

Follow the manufacturer’s dosage instructions, and be careful not to overdose your fish. Complete the recommended course of treatment to prevent your fish from becoming reinfected.

Can Other Treatments Work?

If you don’t want to go down the chemical treatment route, you might prefer to use herbal remedies. In addition, some countries are beginning to restrict the sale of antibiotics for use in the pet trade in an effort to reduce the risk to human and environmental health.

However, I’ve tried some of these treatments on my fish over the years, and to be honest, stronger medications are more effective.

When you’re dealing with serious, potentially fatal conditions, such as Columnaris, it’s really not worth risking a treatment that might not work.

That said, aquarium salt can be a useful complementary treatment for freshwater aquarium fish suffering from white fungus.

Aquarium Salt

Although plecos can be sensitive to salt, you can usually use a mild dose to treat white fungus without harming your fish.

NOTE: Do not use marine salt, Epsom salt, rock salt, or regular salt in your fish tank. Only use aquarium salt!

Salt works by dehydrating the disease-causing organism.

As the salinity of the tank water is increased, water is sucked out of the fungus, parasite, or bacteria by osmosis as the organism tries to rebalance the salt concentration on either side of its skin or membrane.

The harmful microorganisms dehydrate and die quickly, leaving their host disease-free.

Most disease-causing organisms can be successfully treated with salt, although some pathogens are more resilient to it, in which case drug treatment is more likely to be effective.

Treatment Method

Begin by using 1 tablespoon of salt per 3 gallons of water.

I recommend dissolving the salt in a small bowl or cup of water and then pouring it into your aquarium.

This dosage level is pretty low, so it won’t harm your fish. However, most aquatic plants are sensitive to salt, so it’s best to treat your fish in a quarantine tank if you have live plants in your setup.

At low levels, salt fights mild fungal and bacterial infections, as well as gently irritating the fish’s slime coat. That stimulates the production of mucus that can protect the fish from some microorganisms and parasites.

You should keep the affected fish in the salt bath for up to five days before removing them.

Note that aquarium salt won’t be removed by your filter, and, as the water naturally evaporates, the salt is left behind. For that reason, you must only add salt when you’re carrying out water changes.

After Treatment

When the salt treatment is complete, perform a 30% water change without adding any more salt. Observe your fish for a week to see if the fungal infection has gone.

If the fish remain healthy, perform a further 30% water change without replacing the aquarium salt, and wait a further week.

If the disease comes back, start the salt treatment again, increasing the dose slightly.


Do you still have questions about that nasty white fungus on your pleco? Here are the answers to a few of them!

Q: What Is the White Stuff on My Pleco?

A: There are two possible causes of white growths on your pleco; fish fungus or Columnaris.

Fish fungus is caused by water molds known as oomycetes and is typically caused by poor water conditions or skin damage.

Columnaris is a bacterial disease that manifests as white fluffy growths around the fish’s mouth and head.

Q: How Do I Get Rid of White Fungus in My Fish Tank?

A: White fungus is actually a form of mold that grows on all the surfaces in your aquarium, including plant leaves. Mold generally grows in dirty fish tanks where the water quality is poor.

So, to get rid of that nasty white growth, you must give your fish tank a good clean! Remove any dead fish or decaying plant matter immediately, then perform a partial water change to freshen up the water.

Use an aquarium vacuum cleaner to remove decomposing organic waste from around the bottom of the tank and scrape algae from the viewing panes and decorations.

Test the water to ensure that ammonia and nitrite levels are zero and nitrates are below 20 ppm. If the levels are still too high, carry out another partial water change and test the water again.

Q: What Causes White Fungus on Fish?

A: There are two usual causes for white fungus growing on your fish; Columnaris or fish fungus.

Columnaris is a bacterial disease that causes white or greyish fluffy growths on the fish’s head and around its mouth. Fish fungus is caused by a species of water mold called oomycete.

Q: What Disease Do Plecos Get?

Plecos are pretty hardy fish, although they can suffer from several common fish diseases, including:

  • Ich
  • Fin rot
  • Dropsy
  • Hole-in-Head disease
  • Fish Fungus
  • Columnaris

All these diseases can be successfully treated with over-the-counter medication and good husbandry, provided you spot the problem early and take immediate steps to treat it.

Final Thoughts

I hope you enjoyed our guide to identifying, treating, and preventing white fungus in plecos. If the information was helpful and you successfully cured your fish, please share the article.

White fungus on plecos is caused by either a bacterial infection called Columnaris or by fish fungus, a kind of aquatic mold.

Generally, both these conditions occur because your aquarium is dirty or poorly maintained, stressing your fish and leaving them vulnerable to disease.

In addition, injured fish are likely to be attacked by bacterial or mold infections.

You can prevent your pleco from developing white fungus by keeping your fish tank clean and well-maintained and offering your fish a balanced, high-quality diet.

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