A koi off food for 24+ hours warrants investigation. Most causes are simple, some are serious.
Temperature Drop
Sudden 10°F+ drop suppresses appetite for 24–48 hours. Returns when temperature stabilizes.
Water Quality
Test ammonia, nitrite, pH. Any reading out of normal range suppresses appetite.
Disease Onset
Loss of appetite often precedes visible symptoms. Inspect carefully for flashing, clamped fins, or skin changes.
Stress Events
Recent fish addition, pond cleaning, predator scare. Usually resolves in 2–3 days.