Emergency pH Crash in Koi Pond: Crushed Coral, Baking Soda & Root Cause

10 of 12 koi + 6 of 12 goldfish dead in 24 hrs — pH crash from CO₂ buildup. Crushed coral (30 lbs) + baking soda may buffer, but the real fix is biology, not chemistry.

Why pH Crashed

• Severe overstocking: 24 fish in 1,800 gal = ~30–40" of koi + 12–18" goldfish. At 50 gal/inch, need 2,500+ gal.
• CO₂ accumulation: Fish respiration + bacterial decomposition → carbonic acid → pH drop.
• No plants = no CO₂ uptake.
• Low KH (carbonate hardness) = no buffering capacity.

Emergency Buffering (If Fish Still Alive)

1. Baking soda: 1 cup per 1,000 gal raises KH ~20 ppm. Dissolve, add slowly at waterfall.
2. Crushed coral: In mesh bags in filter/flow — slow, steady KH release.
3. Target KH > 100 ppm (6 dKH) — stabilizes pH 7.5–8.3.
4. Aerate heavily: Drives off CO₂, raises pH naturally.

Permanent Fix: Biology Over Chemistry

• Reduce fish load to sustainable level (rehome or expand pond).
• Add plants: 60% surface cover — lilies, marginals, oxygenators.
• Biofilter with high-surface media — processes waste before it becomes acid.
• Test KH weekly — it's the early warning system.

Why "Never Touch Water" Is Dangerous Advice

In a balanced, understocked, planted pond — yes. In a crowded, plantless system — pH will crash. You're not "messing with nature"; you're correcting a man-made imbalance.

Buffer now. Then fix the biology. Or the next crash kills the survivors.