Sudden Goldfish Deaths in Troughs and Pond After Heavy Rain

Feeder goldfish in horse troughs and a garden pond die overnight after heavy rain. Fish are large (6–7"), unfed, water is well water. No visible distress, bloating, or damage.

Possible Causes

• Coincidence: Two deaths in separate tanks same day is unlikely but possible.
• Rain-related: Runoff contaminants, pH shock, temperature drop, or gas supersaturation.
• Well water change: Rain alters groundwater chemistry (e.g., hydrogen sulfide, CO2).

What NOT to Do

Don’t scrub and restart tanks if the cause is unknown—you’ll lose beneficial biofilm and stress survivors.

Monitor & Test

• Test well water for ammonia, nitrite, pH, H2S.
• Observe remaining fish for 48 hours.
• If no more deaths, treat as anomaly.
• Consider a simple aerator in troughs for gas exchange.

Large, old feeder goldfish are valuable. Investigate before resetting.