How To Cure Columnaris Disease (In 5 Steps)

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Having a problem with Columnaris? This nightmare of a disease can quickly kill your fish if left untreated.

Fortunately, I’m offering you a quick solution on how to cure columnaris disease using easy to find products. This technique is an evolution over the 25 years in the hobby that I have had treating various fish diseases.

In this blog post, I’ll outline the 5 steps you need to do to kick this infection to the curb!

Key Takeaways

  • Columnaris is a gram negative bacterial infection that will kill a fish if left untreated
  • A three prong approach of salt, lower temperature, and Methylene blue is the current go to for curing this disease
  • Poor water quality and stress are the top reasons for this infection to occur
  • Once eradicated, a tank can be contaminated again by new introductions in the tank

Before You Get Started

You will need the following to cure this infection from your fish

  • Aquarium salt
  • Antibiotic medications – Methylene blue or Triple Sulfa (if available in your country)
  • Thermometer (To measure tank temperature)
  • Quarantine Tank (if available)

How To Cure Columnaris: A Step By Step Guide

Now that you have your supplies in order, let’s get started with step 1

Step 1 – Quarantine The Fish

While it is certainly possible to treat the fish inside your display tank, my preference is to treat them in a quarantine tank.  If you cannot set up a quarantine tank in time, you’ll need to treat in the display tank. Note that Methlene blue is known to stain silicone and will affect your system’s beneficial bacteria, which is why I prefer to quarantine.

If you do not quarantine the fish, you should do a 50% water change before any treatment occurs. This will ensure you have ideal water parameters before you add any medications.

Step 2 – Treat The Tank With Salt

You will need to dose the tank with salt. You’ll need to be quite liberal with the dosage and amp it up to 2 and half tablespoons per gallon or 3 cups per 20 gallons. This is a lot of salt and will harm any plants in the tank. Note that some fish like Plecos are sensitive to salt so you will need to take caution with them. Some snails and shrimp are also not tolerate of salt treatment.

Step 3 – Dose With Methylene Blue

When antibiotics like Triple sulfa were available, this would have been my go to. However, since it is no longer available in the US and is hard to find (and expensive), my recommendation is to use Methylene Blue. While this is primarily used to treat fungal diseases, it is also effective for this treatment procedure because it acts as a disinfectant. Use the recommended dosage as stated on the manufacturer’s bottle

Step 4 – Lower Water Temperature

Columnaris spreads rapidly in higher water temperatures. Therefore, lowering the temperature might help. You want to target a temperature of 70 – 72 degrees Fahrenheit.

However, if your fish is accustomed to higher temperatures, it will take some time to adjust to temperature changes. Thus, I recommend lowering the temperature by only 2F every two hours.

Step 5 – Monitor Water Quality And Observe

Columnaris bacteria thrive on organic waste. Therefore, it is essential to keep your tank clean and maintain the recommended water parameters for your fish. Check your water for ammonia, nitrate, nitrite, KH, and GH, and ensure nothing is affecting your fish adversely.

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The observation period for this treatment is 7-10 days. In most cases, if the fish survives, the fish should be cured of columnaris and it should be eliminated from the tank. Anything you use in this tank that is untreated, you will want to sterilize. A solution of bleach or dry out for several days will kill off any remaining infection.

What To Avoid Doing

  • Don’t ignore the condition – treat it quickly. Don’t wait around!
  • Avoid doing water changes. If a water change is made, you will need to re-dose the tank
  • Do not carelessly add fish afterward, consider a quarantine process for new additions going forward to prevent recontamination.

What To Do If Symptoms Are Still Around After 10 Days?

If the infection is stubborn, it’s time to go with a half dosage of meth blue and salt. This is an extreme dosage. Either this will eliminate the disease or your fish will end up passing away. Treatment after 10 days tends to have a low success rate, and we get into a worse case scenario.

Note that this technique I outline does not use antibiotics. There are methods where you can, but I preferred for this post not to include them because the ideal medication isn’t available in the US and this method does have a high success rate.

How To Prevent It

As mentioned earlier, the Columnaris bacteria thrive on organic waste. Therefore, partial water changes every two weeks and regularly test water chemistry to ensure recommended water parameters are some of the best ways to keep the bacterial infection at bay. 

Furthermore, the immune system of your fish should be healthy and strong enough to fight off the bacteria. Strong immunity is a result of eliminating stress factors such as bullying and harassment or water fluctuations from your aquarium. It is also recommended to clean up the fish waste and decaying plant matter and gravel to foster a hygienic environment for your fish. 

Also, overcrowding, tank size, and tank mates should be taken into consideration because these factors directly impact the stress levels in your fish. Additionally, a balanced diet with occasional treats might help keep the infection at bay. 

What Exactly Is This Disease?

Columnaris disease is common among freshwater fish, particularly among livebearers fish such as guppy fish, Molly, etc. This disease is mainly caused by Columnaris bacteria that are long and rod-shaped; appearance-wise.

NameFlexibacter columnaris
Common TreatmentsSalt and antibiotics
Short-Term TreatmentAntibiotics
CausesTransferred from infected fish, plants, and water
Treatment Time7 – 10 days
Common SymptomsSaddleback-like growth, lesions on body, mouth, infected gills

Columnaris disease is commonly known as saddleback disease, guppy disease, cotton wool disease, and cotton mouth disease. In brackish and saltwater the species Flexibacter maritimus is the equivalent and is more severe, though not common to see in aquariums.

What Are The Symptoms?

Columnaris is often mistaken as a fungal infection because the fish might show signs of mold-like lesions on their bodies. However, Columnaris is caused by bacterial infection and forms lesions that progress gradually and end up killing the entire freshwater fish population in your tank, if left untreated.

Some of the common symptoms of Columnaris are:

  1. Grey or white spots on the head, fins, and gills
  2. Infected gill tissue
  3. Lesions on the body
  4. Lesions on the mouth area or puffy lips
  5. Frayed, bleached out, and ragged fish’s fins

One of the first signs you’ll notice is frayed or ragged fins, commonly referred to as fin rotHowever, not all fish experience fin rot and may show some other symptoms. For instance grayish or whitish spots of patches on the head or gills.

Sometimes, the lesions on your fish extend down to the sides, giving it the appearance of a saddle near the dorsal fin, and that’s why the common name for Columnaris disease is “saddleback disease”. Ultimately, as the bacterial infection progresses you may notice some other external changes in your fish such as moldy lesions around the mouth and frayed fins. Once the saddleback symptoms occur, a fish will usually survive 1-2 day days if left untreated until ultimately passing away.

However, not all symptoms are external. Some are behaviors that make your fish look more lethargic and weak, with a loss of appetite and hanging out at the surface of water.

What Are The Causes ?

The main culprit of the cotton wool disease or saddleback disease is a bacterial infection that particularly affects freshwater fish’s gills. Some of the major causes of columnaris disease in freshwater fish are:

1. Poor water quality

One of the main reasons your young fish might get Columnaris is poor water quality that compromises the overall health of your fish. 

High levels of ammonia, nitrates, and other pollutants can contaminate your entire tank water and induce stress in fish. Stress messes up the immune system of your fish, making them susceptible to fatal diseases like Columnaris. 

2. Stress 

As mentioned earlier, stress weakens the immunity system of your fish, making it more prone to diseases. Avoid overcrowding, choose suitable tank mates, and feed a balanced diet to eliminate stress in your aquarium. 

3. Injury

Fish with injuries in the form of wounds and lesions are more vulnerable to bacterial infections because Columnaris usually enter the fish through open wounds and lesions on the skin, gills, or fish’s mouth. 

4. Fluctuating water temperature

Studies suggest that fluctuating water temperature influences the metabolic rate of bacteria and affects their growth activity1. Columnaris are mostly associated with warmer temperatures. Therefore, maintaining a stable water temperature for specific fish in your aquarium might help prevent Columnaris and bacterial proliferation. 

5. Untidy tank 

Columnaris bacteria thrive on uneaten food, fish waste, decaying plant matter, dead fish, waste products, and overall a contaminated tank with lots of pollutants. Therefore, it’s crucial to keep your tank clean with pristine water conditions for a healthy ecosystem. 

6. Poor nutrition

A balanced diet means a healthy immune system. A healthy immune system means a strong fight against bacterial and fungal infections. 

Feeding your fish a varied diet, rich in proteins and occasional treats is important to keep the livestock healthy and happy for a long period of time. 

7. Introducing New Livestock To The Tank

If you want to introduce a new fish into your tank, think again!

Because you never know what the fish might bring into your super healthy and playful aquarium. Quarantining a new fish into a separate tank is the most reasonable idea to avoid big problems such as Columnaris and other fish diseases. 

How Does It Enter Your Fish’s Body?

Columnaris strikes when the fish’s immune system is not strong enough to fight the bacteria. The bacteria can enter your fish’s body through gills, mouth, or small wounds on the skin. Therefore, the physical health of your fish is trivial to ensure the overall health. 

The cotton wool disease or saddle back disease is often spread through contaminated fish nets, containers, and uneaten food. Since the disease is highly contagious, it’s always recommended to sterilize your tank decorations or equipment to keep everything in prime condition. 


Columnaris disease is common in freshwater and tropical fish at water temperatures above 15°C or 59°F. At higher water temperatures, the progress of Columnaris disease is faster. Therefore, it is suggested to keep the water temperature low and stable throughout the year. Also, Columnaris bacteria love fish waste, dead fish, and organic waste. Therefore, proper filtration and weekly water changes should be done to prevent Columnaris in the long run. A good quarantine practice should prevent the problem entirely. 

Have any questions for me? Leave a comment in the comments below. I’m also leaving an FAQs section asked by some readers so you can review them as well. Thanks for reading and see you next time!


How long can a fish survive with Columnaris?

The survival time of a fish with Columnaris depends on a number of factors. For instance, the severity of the infection, the presence of other stressors in your aquarium, and the overall health of your fish. The fish with the strongest immune system fight off the disease better than others. Therefore, it is important to understand the factors that may affect the lifespan of your fish in general. 

In some cases, Columnaris can cause instant death of your fish within a short period. It’s especially true if the infection is advanced and not treated properly. However, most cases of Columnaris can be treated successfully if diagnosed early with appropriate treatment. 

However, if your fish is already stressed or suffering from other health issues, it may have a hard time fighting off this disease. Therefore, it is important to monitor water quality and perform water changes regularly. Also, feed your fish a balanced, nutritious diet to support a healthy immune system. 

All in all, consult a professional before treating your fish or administering any special medicine for Columnaris.

Can fish survive Columnaris?

It depends on many factors such as the severity of the infection, the health of the fish, the effectiveness of the treatment provided, and if it is caught early.

Nonetheless, it is a highly contagious disease that requires swift intervention. Some of the factors that may help in the survival of your fish include:

  1. Early detection by recognizing the symptoms of the diseases and starting the treatment promptly. The longer the infection progresses, the less chances of survival for your fish. 
  2. Maintaining aquarium water quality and tank conditions by providing a stress-free environment is essential for the overall immune function of your fish.
  3. Isolating the infected fish from the healthy ones can prevent the spread of the disease for more focused treatment 

Is columnaris a fungal or bacterial disease?

Many aquarists confuse Columnaris with a fungal infection. However, the causative agent of Columnaris disease is a bacteria named, Flavobacterium columnare, which is a gram negative bacteria affecting various freshwater fish. 

You can easily spot a fish with Columnaris disease by the presence of white, thread-like lesions on the skin, fins, and gills. And while Columnaris is a bacterial infection, it may give birth to many fungal infections.

Can salt cure columnaris?

Yes it can when done correctly. This blog post outlined a simple solution of using a hard dosage of salt to cure columnaris. It can be used to eliminate the disease as long as it is caught early.

How do you diagnose Columnaris disease?

Columnaris disease begins as external infections as lesions on the body surface and gills. However, the type of lesions depends on the fish. In catfish, some of the external symptoms are small and circular lesions with gray blue centers and red margins. However, in scaled fish, the lesions begin on the outer margins of the fins and gradually spread throughout their bodies. 

Some behavioral signs of Columnaris include lethargy, loss of appetite, erratic swimming patterns, scratching, and rubbing against the surface to aid discomfort. 

One of the obvious areas of examination is the fish’s gills. That’s because Columnaris directly affects the gills and may show signs of inflammation, discoloration, or excessive mucus production. 

Is Columnaris treatable?

As fatal and contagious as it may seem, Columnaris is definitely treatable with the right medications, early detection, and prompt intervention. 

How to treat columnaris in betta fish?

Treating Columnaris in betta fish is pretty much the same as treating any other fish. Use the same steps outlined in the post for betta fish. It should work the same with them. The main issue with bettas is the water temperatures, but Bettas can tolerate lower temperatures for longer than this treatment calls for.

How to disinfect aquarium equipment after each use?

While treating Columnaris outbreaks in your tropical fish tank, it is recommended to sterilize or disinfect all the tank decorations and other equipment after each use. For this, you can use the commercial treatment of Benzalkonium Chloride solution (Net Soak or Net Dip). Or you can also use hydrogen peroxide, and dip all of your tank decorations in 3% solution. 

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