Essential Winter Pond Care for Healthy Fish

That Pond Guy, a local pond specialist, observes that winter creates difficult conditions for aquatic life, requiring proactive seasonal maintenance alongside proper equipment.

Having assisted numerous clients with winter preparations, he notes that fish from poorly winterized ponds typically face the most challenges come spring. Essential tools for maintaining oxygen levels during this period include Evolution Aqua air pumps.

1. Adjust Water Levels Strategically

Autumn rains combined with reduced evaporation often overfill ponds. Lower water levels to about 4 inches below the rim to prevent overflow. Use your filter’s backwash function if available, or siphon out excess water.

That Pond Guy advises conducting weekly inspections, having witnessed ponds freeze completely due to overflow, which can ultimately damage the liners.

2. Give Filters a Seasonal Service

While fish produce less waste in cold weather, decomposing organic matter still threatens water quality. Clean filter media thoroughly but avoid sterilizing—preserve beneficial bacteria. Position filters in shallower areas to prevent disturbing the warmer bottom layer where fish hibernate.

3. Wage War on Falling Leaves

A single oak tree can drop 10,000 leaves annually—many landing in ponds.

Skim daily with a net to prevent:

• Water fouling from decomposing vegetation
• Pump blockages
• Toxic gas buildup under ice.

4. Install Protective Netting

Pond nets serve dual purposes:

• Catches 90% of falling debris
• Deters hungry herons (winter increases predation risk).

Choose UV-stable mesh with fine enough weave to catch small twigs and berries.

5. Winterize UV Clarifiers

Most UV units are not frost-proof.

In sub-zero temperatures:

• Inspect quartz sleeves for ice damage
• Disconnect and store dry.

Replace bulbs in spring (they lose effectiveness after 6-8 months).

6. Reposition Pumps for Thermal Protection

Fish survive winter by congregating in warmer deep water.

Keep pumps:

• In shallower zones (under 18″ depth)
• Running continuously to prevent freezing
• Away from the pond’s thermal refuge.

That Pond Guy recounts a cautionary incident where a client’s valuable koi perished after their deep-water pump circulated frigid surface water, dangerously lowering the pond’s thermal refuge temperature.

7. Transition Fish Diets Gradually

As water temperatures dip below 10°C (50°F):

• Switch to wheatgerm-based food (easier digestion)
• Reduce portions by 75%
• Cease feeding entirely below 4°C (39°F).

That Pond Guy explains that fish metabolism nearly hibernates, causing undigested food to decay internally.

8. Monitor Water Temperatures Religiously

Invest in a submersible pond thermometer.

Key thresholds:

• 10°C: Switch to winter food
• 7°C: Stop introducing new fish
• 4°C: Suspend all feeding.

9. Consider Heating Options

For serious hobbyists:

• Inline heaters maintain stable temperatures (ideal for show koi)
• Floating de-icers prevent complete freezing (budget-friendly)

Aerators like Evolution Aqua air pumps prevent surface ice while oxygenating.

10. Maintain Gas Exchange

Never let ice fully seal the pond surface.

Options include:

• Floating ice preventers (no electricity)
• Air stones on timers
• Small water features kept running.

That Pond Guy’s Pro Tip: “A simple tennis ball floating on the surface prevents complete ice-over and is easily removed to check water conditions.”

Bonus: Emergency Preparedness

Keep these winter essentials on hand:

• Pond-safe salt for stress relief
• Spare air stones and tubing
• Battery-powered aerator for power outages.

That Pond Guy emphasizes that ponds don’t require perfection, just regular maintenance of essential practices, noting that fish thrive in spring when owners prepare properly during winter.