Fin rot is a bacterial infection that attacks fin edges, producing ragged, frayed, or receding fins. Almost always caused by poor water quality or stress weakening the fish's immune response.
Causative organism: Bacterial (typically Aeromonas, Pseudomonas)
Severity: Moderate (treatable if caught early)
Test ammonia, nitrite, nitrate. Do a 50% water change. Most fin rot resolves with water quality alone if caught early.
Sometimes "fin rot" is actually fin nipping by aggressive tank mates. Watch the tank for 30 minutes - rule out behavioral cause before treating bacterial.
For mild cases. Melafix is plant-extract based and gentle. ParaGuard treats broader-spectrum bacterial issues.
Kanamycin (Kanaplex) or erythromycin (Maracyn) for established gram-negative bacterial infections. Treat for 5-7 days. Remove carbon during treatment.
Antibiotics damage beneficial bacteria in display tanks. Move infected fish to a hospital tank for antibiotic treatment if practical.
Antibiotics kill nitrifying bacteria. After treatment, dose Dr. Tim's One and Only or Fritz Turbo Start to re-establish biological filtration.
Fin Rot is preventable in 95%+ of cases by running a 4-6 week quarantine on every new fish before introduction. Read the quarantine protocol.