Dead Koi After Spring Startup: Salt or Not?

After turning on filter/pump and cleaning pond, one koi found dead. Owner asks if adding salt to kill parasites is advisable.

Assess Before Treating

A single dead fish after winter startup can stem from: cold stress, latent disease, poor winter conditions, or water quality shift. Salt (0.1–0.3%) reduces some parasites but can harm fish with compromised slime coats or gill function.

Better Spring Protocol

1. Run filter gently through winter (or restart slowly in spring).
2. Partial water change (10–20%) after ice-out to dilute metabolites.
3. Add beneficial bacteria to jump-start biofiltration.
4. Observe population for flashing, isolation, clamped fins, lesions.
5. Test water: ammonia, nitrite, pH, KH.

Only treat if multiple fish show symptoms or scrapes confirm parasites. One death warrants monitoring, not blind medication.