Columnaris is a deadly bacterial infection that hits stressed freshwater fish. Often called "cotton wool disease" due to fluffy white patches on the body. Spreads fast and kills within 48-72 hours.
Causative organism: Flavobacterium columnare
Severity: High mortality (fast-moving)
Columnaris thrives at warmer temperatures (78°F+). Lower tank temperature to 75-76°F if possible. Slows pathogen replication.
Salt helps reduce osmotic stress on infected fish and slows columnaris. NOT for soft-water species (most tetras, discus, apistos) at high concentration.
The standard combination treatment. Kanamycin attacks bacterial cell wall; nitrofurazone (Furan-2) attacks bacterial protein synthesis. Both together cover the gram-negative columnaris.
Continue dosing both medications per package directions for at least 7 days, ideally 10. Remove activated carbon during treatment.
After treatment, do a 50% water change with new dechlorinated water. Re-add fresh activated carbon for 48 hours to clear residual medication.
Columnaris is preventable in 95%+ of cases by running a 4-6 week quarantine on every new fish before introduction. Read the quarantine protocol.