Columnaris in Koi: Identification, Rapid Progression, and a Proven Treatment Protocol
Columnaris is one of the fastest-moving and most destructive bacterial infections seen in koi, especially in warm water conditions. It is commonly misidentified as fungus or mouth rot, but when left untreated, it can progress rapidly and cause significant losses — particularly in smaller fish.
This guide outlines how Columnaris presents, why it escalates so quickly, and the exact treatment protocol I use based on real-world outcomes, not theory.
Part of our complete Koi Diseases & Treatment Guide.
What Columnaris Really Is
Columnaris is a bacterial infection, not a fungus, even though it often appears cottony or white. It thrives in warm water, high organic load, and stressed systems, and it spreads quickly across damaged tissue.
It commonly presents as:
White or gray patches on the mouth, head, or body
Erosion around the mouth (“mouth rot”)
Rapid tissue breakdown
Lethargy and loss of appetite
Columnaris often follows parasite damage or minor wounds, which is why early intervention matters.
Why Columnaris Escalates So Quickly
Columnaris does not usually start as a primary problem.
It takes advantage of:
Parasite irritation
Open wounds
Compromised slime coat
Warm water temperatures
Once established, it spreads aggressively and can overwhelm fish before hobbyists realize what they are dealing with.
My Treatment Philosophy for Columnaris
When I see Columnaris starting to form, my first step is always the same.
I begin with a PP-based treatment, such as Purple Magic.
This accomplishes three critical things:
Cleanses parasite populations if any are present
Burns down surface Columnaris bacteria
Cleans and oxidizes any open wounds
Columnaris rarely exists in isolation. Resetting the fish and the environment first gives every treatment that follows a better chance of working.
Proven Columnaris Treatment Protocol
This protocol is based on outcomes that trace directly back to the early development of Bacterial Blast.
Step 1 – Parasite & Surface Reset
Treat the system with a PP-based product to:
Reduce parasite pressure
Lower bacterial load
Clean damaged tissue
Once complete, move immediately to supportive care.
Step 2 – Salt and Antibacterial Treatment
After PP treatment, place the fish on:
5 ppt salt
5–10 g of Bacterial Blast per 100 gallons
This combination:
Reduces osmotic stress
Limits further bacterial invasion
Allows antibacterial treatment to work efficiently
This is where the foundation of Krazy Koi Meds began. After reviewing older research papers and struggling with Columnaris outbreaks in warm August water in Florida — especially in fish under 4 inches — I arrived at this formulation.
The first time I used this specific ratio, I treated the tank and returned a few hours later to find the Columnaris had visibly melted away.
Since implementing this protocol, Columnaris has become a rare issue in my systems.
Step 3 – Structured 48-Hour Cycles
Maintain treatment for 48 hours
Perform a 100% water change
Re-establish 5 ppt salt
Re-dose Bacterial Blast
Repeat this process three times
Total treatment duration: 6 days
Step 4 – Reevaluate
At the end of six days:
Tissue should be stabilizing
Active lesions should be resolving
Fish behavior should be improving
If progress has stalled, reassessment is required before continuing.
Why This Protocol Works
Columnaris requires speed, structure, and consistency.
This approach:
Removes contributing parasite pressure
Controls bacterial growth aggressively
Prevents reinfection between cycles
Allows tissue time to recover
Random or delayed treatments are the main reason Columnaris becomes fatal
