Treatment Protocol for Mouth Fungus (Columnaris / Cotton Mouth)
Treat immediately — mouth fungus progresses fast. Use Kanaplex or Furan-2 in hospital tank. Lower temperature to 75°F to slow bacterial growth. Add aquarium salt (1 tsp per gallon). Improve water quality with daily 25% changes during treatment.
How to Identify This Condition
Look for these symptoms in your fish:
- White cottony growth on mouth or lips
- Erosion of mouth tissue
- Difficulty eating
- Frayed or ragged lips
- White patches spreading to body
Early detection is critical — the sooner you begin treatment, the better the prognosis. Observe your fish daily during routine feeding for any behavioral or physical changes.
Root Causes
Understanding what caused the problem helps you prevent recurrence:
- Flavobacterium columnare bacteria
- Poor water quality
- Stress from aggression or overcrowding
- Injury to mouth area
Recommended Medications
The following medications are effective against Mouth Fungus (Columnaris / Cotton Mouth):
- Kanaplex — follow manufacturer dosing instructions. Treat in a hospital/quarantine tank when possible to avoid disrupting your main tank's biological filtration.
- Furan-2 — follow manufacturer dosing instructions. Treat in a hospital/quarantine tank when possible to avoid disrupting your main tank's biological filtration.
- API E.M. Erythromycin — follow manufacturer dosing instructions. Treat in a hospital/quarantine tank when possible to avoid disrupting your main tank's biological filtration.
- Aquarium salt — follow manufacturer dosing instructions. Treat in a hospital/quarantine tank when possible to avoid disrupting your main tank's biological filtration.
Always have these medications on hand before you need them. See our quarantine tank guide for proper treatment setup.
Water Quality During Treatment
Maintain pristine water conditions during treatment. Perform 25% daily water changes using Seachem Prime as your water conditioner. Remove activated carbon from your filter during medication (carbon absorbs medications). Increase aeration with an air stone — sick fish need extra oxygen. Monitor ammonia and nitrite daily with your test kit.
Recovery & Quarantine
This is a severe condition that requires prompt treatment. Isolate affected fish in a hospital tank if possible. Continue treatment for the full 14-day course. Watch remaining tank mates closely for early signs of infection.
Prevention
The best treatment is prevention. Follow these practices to reduce the risk:
- Maintain stable water parameters
- Avoid aggressive tank mates that nip
- Don't overcrowd
- Quarantine new additions
For a complete prevention strategy, read our quarantine tank guide and maintenance schedule.