Sudden Koi Die-Off: 50% Loss in 12 Hours – Emergency Protocol

Immediate Triage (Do Now)

1. Test ammonia & nitrite (liquid kit). Most likely cause.
2. 50% water change NOW — dechlorinated, temp-matched (within 2°F).
3. Dechlorinator + slime coat (Stress Coat, Prime).
4. Pond salt 0.15% (1.5 cups/200 gal) — reduces nitrite uptake, supports slime coat.
5. Stop all feeding.
6. Max aeration — air pump + stones, waterfall on.

If Ammonia/Nitrite High

• Repeat 25% changes daily until 0.
• Add nitrifying bacteria (FritzZyme 7, Tetra SafeStart) — double dose.
• Ammonia binder (AmQuel+, Prime) as bridge.

If Parameters OK → Toxin Suspect

• Lawn chem runoff? Neighbor spray? Roof tar? New liner off-gas?
• Activated carbon in filter (2 lbs/200 gal) — adsorbs organics.
• Repeat water changes 3× over 48 hrs.

Temperature Shock Warning

Cool weather + cold hose water = thermal shock. Mix hot/cold to match pond temp. Drip-refill if needed.

Monitor & Repeat

Watch for Ich (white spots) — temp drop triggers it. Salt 0.3% treats Ich but harms plants. Quarantine sick fish.