White Slime on All Koi After Ice Melt

After 3 ft snow melt and rain, all koi covered in thick white slime. Waterfall/pump ran, pond not fully frozen. Asks if normal for hibernation.

Not Normal—Action Required

Excess mucus (white slime) indicates severe irritation: parasites (Costia, Chilodonella, Trichodina), bacterial infection, poor water quality, or physical trauma from ice contact.

Diagnostic Steps

1. Check for wounds from ice adhesion (common when fish surface during thaw).
2. Test water: Ammonia, nitrite, pH, KH.
3. Microscopic scrapes: Essential—parasites are the #1 cause of excess slime.
4. If wounds: Clean, disinfect, seal as per wound protocol.
5. If parasites: Targeted treatment (e.g., formalin/malachite green for Costia; praziquantel for flukes).

Do not guess. Fungus is usually secondary. Get a koi vet/dealer to scrape. Treat the cause, not the symptom.