Koi Dying Fast: Pink Skin, Bloody Fins After AlgaeFix Use

4,300-gal pond. Koi show pinkish skin, blood-streaked fins (septicemia). Owner dosed AlgaeFix every 3 days, did water changes. Goldfish unaffected. Koi 12–16 inches, owned 8 years.

Septicemia Causes

• AlgaeFix overdose: Safe at label rate, but repeated dosing + algae die-off can crash oxygen.
• Oxygen depletion: Decaying algae consumes O₂—koi gasp, develop septicemia.
• Water change issues: No dechlorinator? Temperature/pH shock?
• Toxin exposure: Runoff, chemicals.

Emergency Steps

1. Maximize aeration: Air stones, waterfall 24/7.
2. Large water change (30–50%) with dechlorinator + pond salt (0.1%).
3. Add activated carbon to filter.
4. Stop AlgaeFix until crisis resolved.
5. Test oxygen, ammonia, nitrite, pH.

Why Goldfish Survive

Goldfish tolerate lower oxygen and wider parameter swings than koi.

Act fast—septicemia is often fatal once advanced. Aeration and clean water are the only real treatment.