All Koi Died After New Additions: KHV Suspect and Quarantine Protocol

Three koi dead within two weeks of adding two new koi—while 25 goldfish remain unharmed. This pattern strongly suggests Koi Herpesvirus (KHV), a koi-specific pathogen that's 100% fatal to koi but doesn't affect goldfish.

Why KHV Fits

• New koi introduced → died first (carriers often show symptoms under stress).
• Existing koi died subsequently (exposed to virus).
• Goldfish unaffected (KHV is cyprinid-specific but koi are highly susceptible).
• pH 7.9–8.0 is not lethal—KHV kills at normal parameters.

Other Possibilities

• Other koi-specific viruses (carp edema virus, SVC).
• Bacterial septicemia from transport stress, but goldfish would likely be affected.
• Toxin affecting only koi (unlikely).

Immediate Actions

1. Do not add new koi yet. Wait 3–6 months. Goldfish may be asymptomatic carriers.
2. Test goldfish: Contact a koi vet or club for PCR testing for KHV.
3. Disinfect equipment: Nets, tubs, boots with Virkon or bleach (rinse thoroughly).

Future Koi Quarantine Protocol (Mandatory)

1. Separate system: 100+ gallon tank/pond, dedicated equipment.
2. Duration: Minimum 4 weeks, ideally 8 weeks at 70–75°F.
3. Heat therapy (KHV prevention): Maintain 87°F (30.5°C) for 3 weeks during quarantine. This kills KHV. Only do this if you can maintain stable temp and aeration.
4. Salt: 0.1% in quarantine (no plants).
5. Observe daily for lesions, gill necrosis, lethargy, excess mucus.

Pond Salt Levels

• Quarantine (no plants): 0.1% (1 lb/12 gal)
• Main pond (with plants): ≤0.05% (1 lb/25 gal)

When to Restock

If goldfish test negative for KHV and remain healthy for 3+ months, risk is lower. But always quarantine. Source koi from reputable dealers who test and guarantee KHV-free stock.

Losing established koi is devastating. The quarantine discipline you build now prevents future heartbreak.