How to Winterize an Above-Ground Pool in 6 Steps

To winterize an above-ground pool correctly, balance the water chemistry 3 to 7 days before closing, shock the pool the night before, lower the water level 4 to 6 inches below the skimmer, blow out or drain all plumbing lines, remove and store your pump and filter, then install a tight-fitting winter cover. Done right, this takes one afternoon and keeps your pool clean, your liner intact, and your equipment functional for next season.

Skipping steps or rushing the close is the number one reason people open a swamp in spring. A little extra effort in October saves you hours of algae scrubbing in May. If you want a preview of what you are working toward, check out this Spring Pool Opening: A Step-by-Step Walkthrough so you know what a properly closed pool looks like when it wakes up.

Step 1: Balance Your Water Chemistry 3 to 7 Days Before Closing

Before you add any winterizing products, your water needs to be in the right range. Closing on unbalanced water locks in problems for months. Target these levels in the week before closing:

pH: 7.2 to 7.6
Total Alkalinity: 80 to 120 ppm
Calcium Hardness: 175 to 225 ppm
Cyanuric Acid (CYA): 30 to 50 ppm

High pH going into winter leads to scale buildup on your liner and equipment. Low alkalinity makes pH swing all winter long, etching your liner from the inside. Get these dialed in first – everything else you add works better on a balanced base.

Step 2: Shock the Pool the Night Before Closing

Add 2 lbs of calcium hypochlorite shock per 10,000 gallons of water the evening before your closing day. Run the pump overnight so the shock circulates fully through the water. The goal is to kill off any bacteria or early-stage algae before the cover goes on and sunlight disappears for the season.

Do not add algaecide at the same time as shock – the shock will break down the algaecide before it has a chance to work. Wait until the next morning when chlorine levels have dropped back below 5 ppm, then add your winter algaecide. A polyquat 60 algaecide works better for winterizing than the cheap copper-based formulas, which can stain liners if chlorine levels fluctuate.

Step 3: Lower the Water Level

Lower the pool water 4 to 6 inches below the skimmer opening. This keeps water out of the skimmer and return lines, where it would freeze and crack fittings. Use a submersible pump or your filter’s waste setting to drain it down – not all the way, just enough to clear the skimmer.

Never fully drain an above-ground pool for winter. The water inside actually supports the pool walls and liner against wind pressure and ground movement. An empty above-ground pool in a windstorm can collapse or shift, and a dry liner exposed to cold becomes brittle and prone to cracking at the seams.

Step 4: Remove, Drain, and Store the Equipment

This is the step most first-timers skip or halfhearted, and it is the one that causes the most expensive damage. Frozen water expands with enough force to crack pump housings, filter tanks, and heater manifolds.

Remove the pump and filter from their fittings and take them indoors or into a garage.
Drain all water from the pump strainer basket and filter tank.
If you have a sand filter, open the drain plug at the bottom and leave it open through winter.
Remove all hoses and store them flat – hoses left coiled in freezing temps crack at the bends.
Drain and plug the skimmer line with a Gizzmo or a rubber expansion plug. This protects the skimmer from freeze damage far better than just draining the water level.
Plug the return jet opening with an expansion plug rated for your fitting size (typically 1.5 inch).

If you have any water features, LED light fixtures with plumbing, or a heater attached to the pool, the same principle applies to those lines. The How to Winterize Hot Tub Plumbing for Freeze Protection guide covers blow-out techniques in more detail if your setup has tight plumbing runs you cannot fully gravity drain.

Step 5: Add a Winter Enzyme Product

This step is optional but genuinely worth doing. A winter enzyme product breaks down non-living organic material – sunscreen residue, body oils, leaf tannins – that accumulates under the cover over several months. Without it, that organic load oxidizes and leaves a stubborn ring at the waterline and a cloudy mess in spring.

AquaDoc makes a winterizing enzyme product that pool owners use specifically for this purpose – a single dose added after shocking keeps the water cleaner through the dormant season. Add the enzyme the morning of closing after your chlorine has dropped, not with the shock.

Step 6: Install the Winter Cover Properly

A loose or poorly secured winter cover is worse than no cover at all. Wind-driven debris gets underneath, water accumulates on top and tears the cover, and an improperly seated cover can actually pull down the pool walls.

Use a cover specifically sized for above-ground pools with a cable-and-winch system around the top rail.
Tighten the cable so the cover sits flush against the pool wall – no gaps, no billowing edges.
Place a cover pump or cover pillow in the center. A cover pillow (air pillow) floats under the cover and prevents a massive ice sheet from forming that could damage the walls. A cover pump removes standing water so the cover does not sag and tear.
Check the cover after the first big wind storm and re-tighten if needed.

One common mistake: people lay the cover on before the air pillow is inflated and centered. Inflate the pillow to about 60 percent capacity (fully inflated pillows pop in cold weather), tie it to the center return jet, then lay the cover over it.

What to Check Midwinter

Closing the pool is not truly a set-it-and-forget-it job. Ice, debris, and heavy snowfall can shift a cover, split a seam, or let contaminated water pool on top in ways that cause problems. A quick visual check every few weeks takes five minutes. If standing water on top of the cover exceeds a few inches, pump it off before the weight stresses the cover. For a deeper look at what to monitor through the off-season, the Mid-Winter Pool Checks That Save You Money in Spring guide is worth bookmarking now.

Frequently Asked Questions

When should I close my above-ground pool for winter?

Close when your water temperature consistently drops below 60°F (about 15°C). Closing too early while water is still warm invites algae growth under the cover, since warmer water supports algae even without sunlight.

How much shock should I add when closing an above-ground pool?

Add 2 lbs of calcium hypochlorite shock per 10,000 gallons of water the night before closing. Let it circulate overnight, then test the next morning to confirm chlorine has dropped below 5 ppm before adding algaecide.

Should I drain my above-ground pool for winter?

No – leave water in the pool. Water supports the walls and liner through freeze-thaw cycles. Only lower the water level 4 to 6 inches below the skimmer opening to keep the plumbing lines clear.

Do I need a closing kit for my above-ground pool?

A closing kit with shock, algaecide, and a winterizing enzyme product is the easiest way to get the chemistry right. Each product serves a specific purpose, so skipping any one of them usually shows up in spring as algae or a waterline stain.

What happens if I don’t remove the skimmer before winter?

Water trapped inside the skimmer will freeze, expand, and crack the skimmer housing. A cracked skimmer can cost $50 to $150 to replace, and it is entirely preventable by draining and plugging the skimmer line before temperatures drop.

A properly closed pool opens clean, clear, and ready in spring with far less chemical work. The whole process takes three to four hours the first time you do it, and about half that once you have done it once. That is a good afternoon’s work for five months of worry-free off-season.