Columnaris Treatment, Symptoms, & Disease

Columnaris is a highly contagious bacterial infection caused by the bacterium Flavobacterium columnare, which is naturally present in most aquariums. The disease is often referred to as:

• Cotton wool disease – due to the fluffy, white, mold-like patches it can create
• Saddleback disease – due to characteristic lesions near the dorsal fin
• Flexibacter infection – an older term from a former genus name

Why It’s Dangerous

While the bacteria are common, they usually only become a problem when a fish’s immune system is compromised—often due to poor water conditions, stress, injury, or sudden changes in the tank environment.

Columnaris can progress very rapidly, sometimes killing a fish within 24–72 hours if left untreated. Early detection and immediate intervention are critical and one of the first things to do is to test the water!

Symptoms of Columnaris in Bettas

Flexibacter columnaris, also known as columnaris or cotton wool disease, typically shows the following symptoms:

• White or grayish cotton-like growths on the body, fins, or mouth
• Redness or inflammation of the skin and fins
• Fin rot (frayed or disintegrating fins)
• Lethargy and loss of appetite
• Difficulty breathing or gasping at the surface
• Skin ulcers or lesions

Water Testing Helps Identify the Root Cause

Columnaris is opportunistic—meaning it often infects fish when they’re already stressed or immunocompromised. One of the most common stressors? Poor water quality.
By testing your aquarium water, you’re checking for:

• Ammonia – should be 0 ppm

• Nitrites – should be 0 ppm

• Nitrates – ideally under 20–40 ppm

• pH levels – should be stable, typically around 6.5–7.5 for bettas

• Temperature – should be stable (76–80°F)

If any of these are out of range, they could be triggering the infection or making it worse. Treating the disease without fixing the root cause means your fish could get sick again—or not heal properly.

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Causes and Risk Factors of Columnaris & Betta Fish Cotton Wool

Several factors can contribute to columnaris outbreaks in betta fish:

• Poor water quality: High ammonia or nitrite levels, low pH levels, and fluctuating temperatures can stress bettas and increase their susceptibility to infections. Check your water quality using a testing kit.
• Stress: Overcrowding, aggressive tank mates, sudden environmental changes, and poor nutrition can weaken a betta’s immune system.
• Injury: Open wounds or abrasions provide a point of entry for bacteria.
• Betta’s anatomy: Their long, flowing fins and delicate skin make them more vulnerable to infections.

Treating Columnaris in Betta Fish

• Isolate the fish: Move the affected betta to a clean quarantine tank with appropriate water parameters and filtration.
• Start medication: Get API PIMAFIX, which is designed to rapidly treat fungal infections using an all-natural extract from West Indian Bay Trees.

Click here to learn more about Pimafix

• Perform water changes: Change 50% of the water daily during treatment and maintain optimal water parameters with a testing kit.
• Monitor the fish: Observe the betta closely for signs of improvement or worsening symptoms. Adjust treatment as needed.
• Continue treatment: Complete the full course of medication even if the fish appears to have recovered.
• Prevent reinfection: Maintain excellent water quality, minimize stress, and quarantine new fish to prevent future outbreaks.

Columnaris Treatment Options

• Antibiotics: The most effective treatment for columnaris is antibiotics. Kanamycin, furan-2, and erythromycin are commonly used. Follow the dosage instructions exactly and complete the full course of treatment.
  •  Antibiotics:
    • Kanamycin & Furan-2: 7-10 days
      • Why not longer:
        • Antibiotic Resistance: Overuse or prolonged use of antibiotics can lead to antibiotic-resistant bacteria, making future infections more difficult to treat. Kanaplex is another popular option.
        • Organ Damage: Extended exposure to antibiotics can potentially damage the fish’s internal organs, such as the liver and kidneys.
        • Disruption of Beneficial Bacteria: Antibiotics can also harm beneficial bacteria in the fish’s gut and in the aquarium, potentially leading to digestive issues and imbalances in the nitrogen cycle.
    • Maracyn-Two: 5-7 days (Often used in conjunction with another antibiotic, so the total duration may be longer)
      • Why not longer:
        • Similar risks to other antibiotics: While Maracyn-Two is generally considered safe for fish, prolonged use can still lead to antibiotic resistance, organ damage, and disruption of beneficial bacteria.
• Antibacterial Baths: These can be used in conjunction with antibiotics or as a standalone treatment for mild cases. Prepare a bath with a suitable antibacterial medication and follow the instructions on the label.
• Water Changes: Frequent water changes (50% daily) are essential for removing bacteria and waste products from the tank, promoting healing, and preventing reinfection.
• Aquarium Epsom salt: Adding aquarium salt can help reduce stress, improve gill function, and create a less hospitable environment for bacteria.

Preventing Columnaris

The best way to deal with columnaris is to prevent it from happening in the first place. Follow these tips to keep your betta healthy and free from infection:

• Maintain optimal water quality: Test your water regularly with a testing kit and keep ammonia, nitrite, and nitrate levels at zero. Maintain a stable temperature and pH within the ideal range for bettas.
• Quarantine new fish: Quarantine them in a separate tank for at least two weeks. This will allow you to observe for any signs of illness and prevent the spread of disease to your established fish.
• Minimize stress: Provide your betta with a spacious tank, plenty of hiding places, and a varied diet. Avoid overcrowding and aggressive tank mates. Make gradual changes to their environment and avoid sudden fluctuations in water temperature.