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Reduce Water Flow: Decrease pump flow to 30–40% of normal levels, maintaining only slight water movement.
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Control Aeration: Switch air pumps to intermittent mode (on for 30 minutes every 2 hours) or set to the lowest setting.
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Complete Fasting: Stop all feeding when water temperature drops to ≤8℃ to avoid digestive burden.
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Reduce Water Changes: Change water once every 10–15 days, each time not exceeding 10% of the total volume.
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Maintain Quiet: Avoid tapping on the pond walls, reduce activity near the pond, and partially cover the surface to block light.
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Insulate Against Cold: In northern regions, cover the pond with insulation film to keep bottom water temperature ≥4℃.
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Monthly Checks: Quickly test ammonia levels (should be <0.1 mg/L) and check for signs of saprolegnia (water mold) infection.
Key Principle: Minimize all disturbances, allowing koi to overwinter quietly in a stable environment. Gradually resume feeding and normal water flow only after spring water temperatures consistently rise above 12℃.
