To winterize an above-ground pool, balance your water chemistry, shock the pool, add algaecide, lower the water level 4 to 6 inches below the fittings, disconnect and store your pump and filter indoors, and secure a solid winter cover. Done right, the whole process takes about four to six hours and saves you from a nasty green swamp situation come spring. Here is exactly how to do it.
Most pool owners either close too late (water is already cold, algae is already sneaking in) or skip a step and pay for it in April. The goal of winterizing is simple: stop biological growth, protect your equipment from freeze damage, and keep debris out. The six steps below are in the right order – skip around and you’ll end up redoing work.
Step 1: Test and Balance Your Water Before You Do Anything Else
Start with a full water test at least a week before closing day. You want your chemistry dialed in before you add winter chemicals, not after. Target these ranges before closing: pH between 7.4 and 7.6, total alkalinity between 80 and 120 ppm, and calcium hardness between 175 and 225 ppm. If your pH is off, the shock you add in Step 2 will either dissipate too fast or scale your liner.
If your pool has been running hard all summer, it may need a few days of adjustments to stabilize. Do not rush this step. Good water going into winter means much cleaner water coming out of winter. For more on getting your chemistry tight, the The First 30 Days With Your New Above-Ground Pool post has a solid breakdown of sequencing chemical adjustments that applies just as well to closing as it does to opening.
Step 2: Shock the Pool – and Do It Heavy
Add a full closing dose of chlorine shock the night before you plan to put the cover on. For a standard winter closedown, use at least 2 lbs of calcium hypochlorite shock per 10,000 gallons of water. If you’ve had algae issues this season or your water has been turbid, bump that to 3 lbs per 10,000 gallons. Shocking the night before gives the chlorine time to work and lets the level come down slightly before you seal it under a cover.
Run your pump while the shock circulates, ideally for 8 hours overnight. Do not cover while chlorine is above 5 ppm – it will bleach and degrade even a quality winter cover.
Step 3: Add a Winter Algaecide and Any Other Closing Additives
After the shock has circulated, add a winter algaecide rated for 90-plus days. Use the dose on the label for your pool size – do not cut it short. Some closings also benefit from a phosphate remover (especially if you have trees nearby that drop organic debris into the water all summer) and a metal sequestrant if you have iron or copper in your fill water.
AquaDoc makes a closing kit that covers shock, algaecide, and sequestrant in one package, which simplifies this step if you’d rather not source three separate products. Run the pump for another hour after adding these chemicals so everything distributes evenly.
Step 4: Lower the Water Level
Drain the pool water down to 4 to 6 inches below the skimmer and return fittings. This keeps water out of the plumbing connections so it can’t freeze and crack the fittings or the liner bead. Do not drain the pool completely – an empty liner can shrink, crack, or float out of the track if any groundwater is present. Leave the water in the pool; just get it below the hardware.
Use a submersible pump, your multiport valve’s waste setting, or a siphon hose to drain to the right level. Check local regulations before draining – most municipalities require pool water to be dechlorinated before it hits the storm drain or lawn.
Step 5: Disconnect, Drain, and Store Your Equipment
This is the step most people rush, and it causes the most expensive damage. Remove your pump, filter, hoses, and any inline chlorinator. Drain them completely – water left inside a pump housing or filter tank will freeze and crack the housing. Store everything indoors: a garage, basement, or shed all work fine. Do not leave your pump outside under a tarp and call it good.
If you have a sand filter, drain it via the drain plug at the bottom, then move it inside. If you have a cartridge filter, remove the cartridge, rinse it, and let it dry before storing. Cap or plug all the wall fittings (skimmer and return) with expansion plugs or foam plugs rated for freeze protection. This keeps debris out and provides a small amount of freeze relief at the fittings.
Keeping an eye on things mid-season is worth the five minutes it takes – the Mid-Winter Pool Checks That Save You Money in Spring guide explains exactly what to look for after you’ve closed up.
Step 6: Install Your Winter Cover and Secure It Properly
Use a solid winter cover rated for your pool size, not a solar cover or a tarp. A proper above-ground winter cover will have a cable and winch system that cinches under the pool’s top rail. Thread the cable through the cover’s hem, run it around the entire perimeter, and tighten the winch until the cover is snug but not stretched tight. A cover that’s too slack will sag under rain or snow and collect water in the center – that pooled water is heavy and can collapse an above-ground pool wall.
Use a cover pump or a cover pillow (also called an air pillow) under the center of the cover to prevent water and ice from pooling in the middle. The pillow displaces ice toward the edges of the pool rather than letting a single sheet of ice press against the walls. One standard 4×4 air pillow works for pools up to about 15 feet round; use two for larger pools.
Fair warning: even a well-installed cover will collect some debris over the months. If you open the cover in spring and find a layer of sediment and muck, you are not alone – that situation is common enough that it deserves its own conversation, and Your Winter Cover Is Full Of Filth And Guilt covers exactly how to handle it.
When Should You Close Your Above-Ground Pool?
Close when your water temperature is consistently below 60 degrees Fahrenheit – not when the air temperature drops, but the water temperature. Algae cannot grow effectively below 60 degrees, so closing at or below that threshold means your winter chemicals are doing minimal work the whole time the pool is covered. Closing too early when water is still warm gives algae a head start before your algaecide kicks in. In most of the northern United States, that means closing somewhere between late September and mid-October.
Frequently Asked Questions
How low should I drain my above-ground pool for winter?
Lower the water 4 to 6 inches below the return and skimmer fittings. This keeps water from sitting in the lines and freezing, which can crack fittings or pop the liner off the wall.
What chemicals do I need to winterize an above-ground pool?
You need a pool shock (at least 2 lbs per 10,000 gallons), a winter-rated algaecide, and balanced pH and alkalinity before you close. Some pool owners also add a phosphate remover and a metal sequestrant, especially if they have hard or well water.
Do I need to blow out the lines on an above-ground pool?
Most above-ground pools use flexible hoses rather than buried PVC, so a full blow-out is usually not required. Disconnect the hoses, drain them completely, and store your pump and filter indoors – that handles the freeze risk without needing an air compressor.
When should I close my above-ground pool for winter?
Close when your daily water temperature consistently drops below 60 degrees Fahrenheit. Closing at or below this threshold keeps algae from blooming under the cover all winter long.
Can I leave water in my above-ground pool over winter?
Yes – you should. Leaving water in the pool keeps the liner weighted down so it doesn’t shift, shrink, or crack over the winter. Just lower it to below the fittings, not all the way out.
A clean, well-closed pool is the only thing standing between you and a miserable spring opening. Get the chemistry right, store your equipment inside, and put a real cover on it – and you’ll be swimming again in spring while your neighbors are still scrubbing green walls. That is the whole point of doing this right. For a deeper look at what pool and spa professionals recommend for seasonal maintenance in general, it is worth browsing what the pros think about year-round water care.