Stage 1 — Mild (Edge Decay)
You will see slightly ragged or torn fin edges, sometimes with a faint dark or pale outline. The fish still eats, swims, and behaves normally. Cause is almost always poor water — too long between water changes, ammonia spikes, or low temperature.
Treatment: 50% water change daily for 5 days. Add 1 teaspoon of aquarium salt per gallon. Keep temperature at 79-80°F. Most mild cases heal with no medication in under a week.
Stage 2 — Moderate (Ragged Loss)
Larger chunks missing, fins look chewed or jagged, possible white fuzzy growth at the edges (secondary fungus). Add API Furan-2 or Seachem KanaPlex to the salt and water-change protocol. Treat for the full 7-day course even if you see improvement on day 3.
Stop using carbon during medication — activated carbon removes the medicine before it works. Resume after the treatment ends.
Stage 3 — Severe (Body Reaching)
Rot has eaten down to the body or near the spine. The fish becomes lethargic, stops eating, and may have red or bloody patches. This needs aggressive treatment with broad-spectrum antibiotics like API E.M. Erythromycin combined with Furan-2.
Survival drops sharply at this stage — about 40-50% recover with intensive treatment, the rest succumb to systemic infection. Even survivors may permanently lose fin structure.
Recovery and Regrowth
Fins regrow about 1-2mm per week in healthy water. New growth often appears clear or slightly different in color and gradually darkens. Full recovery takes 4-8 weeks. Maintain pristine water for the entire regrowth period or rot will return.
- ✦Test ammonia and nitrite weekly during recovery.
- ✦Feed less and more often to keep waste low.