Fall-to-Winter Pond Care: Keep Your Koi Pond Safe!

When the leaves begin to fall and the nights in New Jersey turn cold, your pond is entering its most critical season. Fall is the beginning of winter prep for your koi pond. What you do now to prepare will help determine whether your fish thrive or struggle during the winter season.

At Atlantis Water Gardens, we’ve been helping New Jersey residents with pond cleanouts, winterizations, and koi pond construction near me in Randolph for over two decades. We’ve seen ponds that glide through winter without a hitch and the ones that become a springtime nightmare of sludge, fish loss, and expensive equipment repairs.

This blog is your complete fall-to-winter checklist, broken down into steps that keep your koi safe, your water clean, and your equipment protected!

TL;DR – Fall-to-Winter Pond Care Checklist

Here’s the quick version:

• Net & clean debris before it sinks and turns toxic.
• Install pond netting correctly to keep out leaves and predators.
• Adjust koi feeding: wheat germ food under 60°F, stop below 50°F.
• Maintain oxygen & open water with aerators and de-icers.
• Shut down risky equipment like waterfalls, UV clarifiers, and external filters.
• Winterize plants by trimming marginals and sinking hardy lilies.
• Check koi health & water quality before freeze-up.
• Monitor through winter with weekly equipment checks and backup plans.

👉 Follow these steps now, and you’ll enjoy clear water, healthy koi, and fewer headaches when spring returns.

Step 1: Keep Leaves and Debris Out Before They Sink

Leaves might look pretty when they land on the water, but once they sink, trouble begins. As they decompose, they create ammonia spikes, use up oxygen, and fuel spring algae blooms.

Neglecting to clean the leaves from your fish pond is risky, and what you don’t clean up now becomes a toxic mess under the ice.

Your To-Do List:

• ✅ Install a pond net before peak leaf drop. A simple net can keep 90% of leaves out.
• ✅ Skim daily if you missed the netting window. The longer leaves sit, the harder they are to remove.
• ✅ Vacuum or scoop out debris from the bottom. Even a thin layer of muck can stress your pond come spring.
• ✅ Trim back aquatic plants. Marginal grasses and lilies die back in cold weather, cut them now to prevent extra debris.

Skipping this step is the most common mistake we see, and it often leads to cloudy water, foul smells, and even fish kills.

Step 2: Net Your Pond Properly

If you’ve ever pulled up a net sagging with soggy leaves, you know why we’re sticklers for proper installation. Pond netting is simple insurance for your pond’s health, and it does double duty against predators.

Pro Setup Tips:

1. Pick the right net. Choose UV-resistant polyethylene or nylon with ½” mesh. Cheap nets fall apart after one season.
2. Measure carefully. Order a net that covers your pond, stream, and waterfall edges.
3. Tent it. Use PVC hoops or a center pole to create a “roof.” This keeps leaves sliding off instead of piling up.
4. Anchor securely. Stake all sides or tuck under rocks. One open corner is all it takes for leaves to sneak in.
5. Clean weekly. A quick sweep with a blower or broom prevents sagging under heavy leaf loads.

Bonus: A taut net also deters herons, raccoons, and foxes that start hunting ponds when other food sources dry up in late fall.

Step 3: Adjust Feeding Before Winter Dormancy

Your koi’s digestive system is directly tied to water temperature. Once it cools, their metabolism slows. Feed them the wrong food, or feed them too long into the season, and you’ll end up with sick fish and fouled water.

Fall Feeding Rules:

• ✅ Switch to wheat germ-based food below 60°F. It’s easier for koi to digest.
• ✅ Stop feeding below 50°F. At this point, koi go dormant and don’t need food.
• ✅ Stick to 5-minute meals. Only feed what your koi eat quickly. Leftovers rot and create ammonia.
• ✅ Avoid late snacks. Don’t toss in treats once feeding has stopped, their bodies can’t handle it.

Remember: feeding your koi into the 40s doesn’t keep them “happy.” It just fills their bellies with food they can’t digest, which can cause fatal internal issues over winter.

Step 4: Protect Fish with Oxygen and Open Water

When ponds freeze solid, gases from decomposing debris get trapped under the ice. Without a hole for gas exchange, fish suffocate. This is why aerators and de-icers are so important.

Your Oxygen Safety Net:

• ✅ Run an aerator. Place the air stone halfway down, not at the deepest point, so you don’t disturb the warm bottom zone where koi rest.
• ✅ Add a floating de-icer. This keeps a small opening in the ice for gases to escape.
• ✅ Have a backup. A second de-icer or air pump on hand saves the day if one fails.
• ✅ Never hammer ice. The shock can kill fish. If needed, use hot water to melt an opening.

This small effort prevents winter fish kills and keeps your koi stress-free until spring.

Step 5: Shut Down the Right Equipment

Knowing what to run, and what to shut down, can make or break your pond in winter. Too many homeowners let waterfalls run all winter, not realizing the risks.

Shut Down:

• ❌ Waterfall pumps. Ice dams form and divert water out of the pond. We’ve seen ponds drain dangerously low in just hours.
• ❌ External bead or pressure filters. They crack if water inside freezes.
• ❌ UV clarifiers. Not needed in cold weather, and bulbs last longer if stored dry.

Keep Running:

• ✅ Your #1 defense against ice lock.
• ✅ De-icers. Essential for gas exchange.
• ✅ Optional small circulation pumps. Run shallow to prevent surface freeze—but don’t disturb the bottom refuge zone.

Be sure to drain, disconnect, and store shut-down equipment in a frost-free space. Pumps and filters left outside can cost you big in spring repairs.

Step 6: Winterize Plants and Landscaping

Plants don’t get a free pass. If left unmanaged, their die-off adds just as much debris as fallen leaves.

Checklist for Plants:

• ✅ Trim marginals. Cut them down to a few inches above water before frost.
• ✅ Move hardy lilies. Sink them to the deepest part of your pond (at least 2 feet).
• ✅ Remove tropical plants. Store indoors in damp soil or buckets of water until spring.
• ✅ Don’t leave rotting stems. They collapse into the pond and add to the muck.

Healthy, prepped plants mean clearer water and less work next year.

Step 7: Perform a Pre-Freeze Health Check

Your koi can tell you a lot about pond conditions before winter locks things down.

Observation Checklist:

• ✅ Watch where koi gather. If they’re clustered at the waterfall, oxygen may be low in other areas.
• ✅ Look for stress signs. Red streaks, ragged fins, or unusual lethargy should be addressed before ice sets in.
• ✅ Test your water. Check pH, ammonia, and nitrites. Balance now while it’s easy.
• ✅ Fix problems early. Mid-winter is the worst time to try correcting water quality issues.

This is your last window to fine-tune pond health before everything slows to a crawl.

Step 8: Keep an Eye on Things Through Winter

Winter ponding is less about heavy work and more about watchful monitoring.

Winter Watch Routine:

• ✅ Check aerators/de-icers weekly. A quick glance ensures they’re working.
• ✅ Clear heavy snow from nets. Too much weight can collapse them into the pond.
• ✅ Avoid disturbing fish. Let koi rest, they’re conserving energy.
• ✅ Keep spares ready. Backup equipment is a lifesaver if something fails during a storm.

Stable and undisturbed, that’s the winter goal for both fish and equipment.

Prep Now, Relax Later – Atlantis Water Gardens

Your pond is a living ecosystem and a reflection of your investment. By following this fall-to-winter checklist, you’re setting yourself up for a stress-free spring with clear water, healthy koi, and intact equipment.

We know this list can feel like a lot, but don’t worry, you don’t have to tackle it alone. At Atlantis Water Gardens, we’ve winterized thousands of ponds across New Jersey. We know the little details that keep koi safe and ponds beautiful, even when the snow flies.

👉 Ready to get your pond winter-ready? Call us today at 973-627-0515 or contact us online now and schedule your winter service.

Let’s make sure your pond weathers the cold as gracefully as the koi resting beneath the ice.

FAQs About Fall-to-Winter Pond Care

Do I really need to net my pond if I don’t have a lot of trees?

Yes. Even a few leaves can sink, decompose, and fuel algae or ammonia spikes. Netting is cheap insurance against fish stress and water quality issues.

Can I keep my waterfall running all winter?

We don’t recommend it. Ice dams often form, rerouting water out of the pond and draining it dangerously low. Better to shut it down and rely on aeration/de-icing.

How do I know when to stop feeding my koi?

Use a pond thermometer. Switch to wheat germ-based food when the temp falls below 60°F and stop feeding altogether below 50°F. At that point, koi enter dormancy and can’t digest food.

What’s more important for winter, an aerator or a de-icer?

Both have advantages. The aerator provides oxygen, while the de-icer ensures gases can escape. Together, they can help prevent suffocation under ice.

Can I skip winter prep and just clean in spring?

Not safely. Skipping fall prep often leads to fish loss, foul water, equipment damage, and expensive spring repairs. A little effort now saves a lot later.