Isolating a Sick Koi: Step-by-Step

One koi stays at surface, barely moves. Others appear healthy. Owner seeks guidance.

Immediate Triage

1. Test water: pH, ammonia, nitrite, KH, GH.
2. Inspect the fish closely: Look for red areas, ulcers, fungus, parasites, clamped fins, excess mucus.
3. If only one fish affected: Quarantine immediately in a separate tank with pond water, aeration, and mature filter media.
4. Microscopic scrapes: Essential for parasite ID. If unavailable, consult a koi vet/dealer.
5. Treat based on findings: Bacterial → antibiotic; parasitic → targeted antiparasitic; fungal → antifungal; wound → clean/seal.

Do not medicate the main pond blindly. A single sick fish usually indicates an individual issue (injury, stress, low immunity) rather than a pond-wide outbreak.