Sudden Daily Goldfish Deaths in Established 3000-Gallon Koi Pond

Sudden Daily Goldfish Deaths in Established 3000-Gallon Koi Pond

A 10-year-old 3000-gallon koi/goldfish pond suddenly loses 1-2 goldfish daily for two weeks. Water has a yellowish tint. Fed Tetra pond pellets.

Investigation Steps

1. Check for leaf/seed drop from nearby trees (elm, hickory, ash) – tannins cause yellow water; some seeds/nuts toxic.
2. Test water for ammonia, nitrite, pH, KH, GH, oxygen.
3. Examine dead fish for lesions, fungus, parasites, gill damage.
4. Recent additions? New plants, fish, or chemicals?
5. Wildlife activity? Raccoons, herons, etc. causing stress/injury?

Immediate Actions

• Remove yellow water source (net leaves, activated carbon for tannins).
• Partial water change with dechlorinated water.
• Add pond salt (0.05%) and MelaFix as supportive care.
• Consult a local pond specialist for on-site diagnosis.

Sudden mortality in an established pond signals an acute change – find the trigger.