New Pond, Minnows/Tadpoles Added, Then Koi Die: Well Water Toxicity?

14×16 Pond, Well Water, Minnows Added, Koi Die with Slime/Sores

Well water + high hardness/rust/limestone = suspect copper, iron, pH. Minnows/tadpoles tolerate it; koi don't.

Critical Tests

• Copper (pipes) — causes lesions, slime coat shedding.
• Iron — gill damage.
• pH, hardness, alkalinity — exact numbers, not "passed."

Immediate

1. Test copper/iron (lab or strips).
2. 20% water change + dechlorinator + 0.05% salt.
3. Activated carbon in filter.
4. MelaFix for sores.

Resources

Copper Toxicity Info | KoiVet | Local koi club for scrapes.