How To Close Your Above Ground Pool For Winter

We already have a guide on opening your above ground pool in the spring. This is the other end of the season, and if we're being honest, it's the more important of the two.

A good opening saves you a weekend. A good closing saves you a pool.

Everything that goes wrong over winter — a split pump housing, a cracked skimmer, a collapsed wall, a green swamp in April — traces back to something that did or didn't happen on closing day. The process itself isn't complicated. There are about ten steps, most of them take minutes, and once you've done it one time you'll do it in an afternoon every year after.

Here's the whole thing, start to finish, written for someone doing it for the first time.

When to close

Wait for the water temperature, not the calendar.

Close when your water is consistently below about 60°F and staying there. In most of the country that's somewhere between late September and late October, but it varies a lot by region and by year, so buy a cheap floating thermometer and let it make the call.

Closing too early is the most common first-timer mistake. Warm water burns through sanitizer fast. If you seal up a pool at 75°F, your winter chemicals get consumed in the first few weeks and you're guaranteed to pull the cover off an algae bloom next spring. Waiting for cold water is free, and it does more for your spring opening than any product you can buy.

At the other end, don't wait so long that you're doing this in freezing weather. Plumbing that's already frozen is plumbing you can't drain properly.

What you'll need

Gather everything before you start so you're not making a supply run halfway through.

A test kit or test strips
Balancing chemicals (pH increaser/decreaser, alkalinity increaser, calcium hardness increaser as needed)
Pool shock
Winter algaecide
A stain and scale preventer (sequestrant)
Winterizing plugs for your return, and a skimmer plate or skimmer cover
An air pillow sized for your pool
A winter cover, plus cable and winch or cover clips
A cover pump or siphon
Skimmer net, brush, vacuum
Something to store small parts in — a labeled bag or bucket

If you're missing pieces, our above ground pool covers, liner and cover accessories and chemicals collections cover the whole list.

Step 1: Clean the pool thoroughly

Skim the surface, brush every wall surface and the floor, then vacuum. Empty the skimmer and pump baskets.

Do not skip this because "it's going under a cover anyway." Organic debris left in the water is food for algae, and it will spend five months feeding whatever survives your winter chemicals. Leaves sitting on the liner all winter can also stain it permanently.

While you're at it, clear leaves, mulch and grass clippings away from the outside base of the pool too. Wet organic material packed against a steel wall for an entire winter is one of the leading causes of wall rust — more on that at the end of this article.

Step 2: Balance the water

This is the step that actually protects your equipment and your liner, and it's the one people rush.

Test and adjust:

pH: 7.4 to 7.6
Total alkalinity: 80 to 120 ppm
Calcium hardness: most vinyl liner manufacturers ask for roughly 175 to 250 ppm — check your liner documentation

Water that sits all winter on the acidic side is corrosive to metal parts, your ladder, your fittings and your equipment. Water that sits high in pH and hardness leaves scale on everything. Five months is a long time for water to be wrong. Our water testing guide walks through how to read each number if you're new to this.

Let the pump run a few hours after balancing so everything mixes.

Step 3: Shock, then treat

Order matters here.

Shock the pool first and let it circulate. Then, once chlorine has come back down to a normal level, add your winter algaecide and your stain and scale preventer. Adding shock and algaecide at the same time wastes both — the high chlorine level breaks down the algaecide before it can do its job.

Follow the dosing on each label for your pool's gallon count. If you don't know your volume, our team can work it out from your pool's size in about thirty seconds.

Run the filter for several hours after the last chemical goes in.

Step 4: Remove everything that comes out

Take out and store:

The ladder or steps
The skimmer basket and weir door
Solar cover and reel, if you use one — see Solar Pool Covers 101 for storage tips
Floats, toys, thermometer, hoses
Any lights, automatic cleaner, or mineral cartridge
Your salt cell or chlorinator, if you run one

Rinse things with fresh water, dry them, and store them somewhere cool and dry. Ladders left in a freezing pool get destroyed by ice, and they're not cheap to replace.

Step 5: Lower the water — but only a little

You have two options, and both are fine:

Option A: Lower the water to about 4 to 6 inches below the skimmer opening. This gets water out of the skimmer entirely so nothing in there can freeze.

Option B: Leave the water at its normal level and install a skimmer cover plate or skimmer guard over the mouth of the skimmer. This dams the skimmer off while keeping the pool fuller, which many owners prefer.

Which you choose is mostly personal preference and what your climate demands. What matters is that water cannot sit inside your skimmer and freeze. A cracked skimmer is one of the most common winter repairs.

Step 6: Plug the return and seal the skimmer

Remove the return eyeball fitting and install a winterizing plug — a threaded plug or an expansion plug, depending on your fitting. If you're using the skimmer plate method, install it now.

Keep the eyeball, gaskets and small hardware in your labeled parts bag. You will not remember where you put them in May.

Step 7: Drain your equipment completely

This is where freeze damage actually happens, and it's non-negotiable.

Water expands about 9% when it freezes. Any water trapped in a pump housing, filter tank or hose has enough force behind it to split the plastic.

Disconnect the hoses from the pump and filter, drain them, and store them
Pull every drain plug from the pump and the filter tank — most pumps have more than one
With the pump empty, bump it on for a second to clear residual water, then leave it off
On a sand filter, drain the tank and set the multiport valve to the "winterize" or closed position, and remove the pressure gauge
On a cartridge filter, pull the cartridge, hose it clean, dry it and store it indoors
Store your drain plugs in the pump basket so they're with the equipment next spring

If you can, move the pump and filter into a garage, basement or shed for the winter. It's the single easiest way to guarantee they survive.

Step 8: Put in an air pillow

The air pillow floats in the middle of the pool under the cover, and it does two jobs.

First, when the pool surface freezes, the pillow gives the ice somewhere to expand into. Instead of a solid sheet of ice pressing outward on your walls all winter, the pressure is absorbed toward the center. On a steel wall pool this matters.

Second, it creates a high point so rain and melting snow run to the edges of the cover instead of pooling in the middle.

Inflate it to about two-thirds full, not drum tight. An overinflated pillow is much more likely to burst in the cold. Tether it to the pool so it stays centered.

Step 9: Get the cover on properly

Lay the winter cover over the pool with the overlap even all the way around. Run the cable through the cover's grommets and tighten it with the winch, then add cover clips or wall bags for extra security in windy areas.

A cover that's tight and even does its job. A cover that's loose flaps, chafes and eventually shreds — and a flapping cable can abrade the outside of your wall all winter, which starts rust.

Step 10: Put a cover pump on it and check in

Set a cover pump on top of the cover, or plan to siphon regularly.

Water and snow accumulating on the cover is heavier than people expect, and a heavily loaded cover pulls inward on the top rails and wall. This is a real cause of winter damage, and it's completely avoidable.

Check on the pool a few times over the winter — after big storms especially. Pump the cover off, make sure the cable is still tight, and look for tears.

The one thing you should never do

Do not drain your above ground pool for the winter.

New owners think about it every year, and it's the fastest way to lose a pool. Here's why:

The water is what gives your pool stability. An empty above ground pool is a large, light structure that wind can damage or move.
Vinyl liners shrink and stiffen in cold weather. A liner that's drained and left empty over winter very often will not stretch back to fit in spring, and you're buying a new one.
Without water pressure holding it in place, the wall can lose its shape.

Lower the level a few inches if your method calls for it. Never take it down to empty.

A steel wall bonus: closing day is your best inspection window

Since you're already walking the whole perimeter with the equipment off and the water down a few inches, spend ten more minutes doing an annual wall check.

Look at the bottom several inches of the wall all the way around. Look underneath the skimmer and return for rust staining, which usually means a fitting has been weeping. Lift two or three top rails and look at the connector plates and stabilizer bars underneath.

Catching a small rust spot in October means you treat it next spring for a few dollars. Catching it three years later can mean the pool is done. Our steel wall rust guide covers exactly what to look for and what each finding means.

If you don't get a hard freeze

If you live somewhere that stays above freezing, you may not need to close at all. Many owners in mild climates run the pump on a reduced schedule year-round, keep the water balanced, and simply cover the pool to keep debris out.

That's a legitimate approach, and often cheaper than closing and opening. The one thing to watch is unexpected cold snaps — if a hard freeze is in the forecast and your pool is still running, keep the pump circulating through it. Moving water is much harder to freeze than still water.

The short version

Wait until the water is consistently below 60°F
Clean the pool, and clear debris from the outside base too
Balance pH, alkalinity and calcium hardness
Shock first, then add algaecide and stain preventer
Remove the ladder, baskets, accessories and salt cell
Lower water below the skimmer, or install a skimmer plate
Plug the return, seal the skimmer, bag the small parts
Drain the pump, filter and hoses completely — pull every plug
Add an air pillow, inflated about two-thirds
Secure the cover, keep it pumped off, and check it through the winter

And never drain the pool.

Closing day is a few hours of work that decides how your April goes. Do it right once and you'll have the routine forever.