Winterizing a Pool: Step-by-Step Closing Guide
Close your pool when water temperature consistently drops below 65°F, typically late September through early November depending on your region. The full process takes 2-4 hours for DIY and costs $50-$150 in chemicals and supplies. Closing properly prevents freeze damage, algae buildup, and a nasty spring re-opening.
This guide is part of our pool maintenance guide for beginners, a good starting point if this is your first full season as a pool owner.
Is this guide for you?
This guide is for you if:
- You have a seasonal pool in a frost-risk climate (USDA zones 1-6)
- Water temperature is approaching or has dropped below 65°F
- You’re closing for the first time and want a complete checklist
This guide is NOT for you if:
- You live in a year-round warm climate with no freeze risk (minimal off-season steps apply)
- Your pool is green right now, fix the algae before closing, or you’ll seal in the problem
- You just want cost info without doing it yourself, see what professionals charge to close a pool
Video guide
Video: “How to CLOSE an ABOVE GROUND POOL” by Swim University
Tools and supplies you’ll need
Gather everything before you start. Having supplies on hand makes the 2-4 hour process smoother.
Chemicals:
- Pool shock (Cal-Hypo 65% or liquid chlorine), to raise FC to 3-5 ppm the night before closing
- Winter algaecide (polyquat 60 type. NOT copper-based, which stains pool surfaces)
- Metal sequestrant, prevents iron and copper staining while the pool sits under cover
- Winter slow-release floater or pill kit
Equipment:
- Shop vac on blow setting, or air compressor (for plumbing blowout)
- Non-toxic RV antifreeze (backup if full blowout isn’t possible, never use automotive antifreeze)
- Winter cover (solid tarp, mesh safety cover, or solid safety cover)
- Cover anchors, water bags, or cable-and-winch system depending on cover type
- Pool plugs or Gizzmos for skimmer and return lines
- Test kit or test strips
Step 1: balance chemistry one week before closing
Test all parameters before adding a single chemical. Adjusting blind wastes money and throws other parameters off.
Pre-close targets from Pinch A Penny: pH 7.2-7.8, Total Alkalinity 80-120 ppm, Calcium Hardness 175-225 ppm, Free Chlorine 1-3 ppm. These are deliberately wide ranges because stagnant water under a closed cover stays more stable than an active pool.
Why balance a week early? Winter cover creates stagnant conditions. Balanced water resists scale, staining, and algae far better than unbalanced water that then sits undisturbed for months.
Add chemicals in this order: Alkalinity first, then acid (pH down or up), then everything else. Never mix chemicals together. Wait 24 hours after any major chemistry adjustment before adding closing chemicals.
See balancing pool chemistry before closing for the full adjustment guide and the EPA pool operation and maintenance guidelines{:target=“_blank”} for the chemistry basis behind these targets.
Step 2: shock the pool the night before closing
Shock with Cal-Hypo 65% or liquid chlorine the evening before your closing day. Target: raise FC to 3-5 ppm. Higher is fine, it will naturally fade down under the cover over the first few weeks.
Shock at night. UV light degrades chlorine quickly, so daytime shocking wastes product. Run the pump overnight after adding shock to circulate it fully.
Do NOT add winter algaecide the same night as shock. Chlorine destroys algaecide on contact. Add the algaecide the following morning, once FC has had a chance to drop below 5 ppm. This sequencing rule is the one most beginners miss.
Step 3: backwash and clean the filter
Start winter with a clean filter. Organic matter left inside a filter breeds bacteria over months of stagnation.
Sand or DE filter: Backwash fully, then set the multiport valve to the “Closed” or “Winter” position. Remove and store the pressure gauge if your filter is outdoors in a freeze climate.
Cartridge filter: Remove cartridges, clean thoroughly with a cartridge-specific cleaner, let them dry completely, and store indoors. A wet cartridge stored in a cold space can freeze and crack the filter media.
For detailed cleaning instructions, see clean your filter before closing for winter.
Step 4: lower the water level (freeze climates only)
In freeze climates, lower water 4-6 inches below the skimmer mouth. This protects the skimmer throat and return fittings from freeze expansion damage.
Mild climates with no freeze risk can skip this step, leave water at normal operating level.
How to lower water: use the main drain pump setting, or drop a submersible pump into the deep end and run it to a drainage point.
Do NOT drain completely. Water weight holds the pool shell in the ground. Fiberglass and vinyl liner pools are especially vulnerable to “floating” out of the ground when empty, even a heavy rainstorm can push an empty fiberglass pool upward if the soil is saturated.
Step 5: blow out plumbing lines
This is the most commonly skipped step and the most expensive mistake in winterizing a pool.
Water trapped in pipes expands when frozen. That expansion cracks pipes, fittings, and equipment. Repair costs run $500-$2,000 come spring, far more than hiring a professional closer for this one step.
How to blow out lines:
- Attach shop vac (blow setting) or air compressor to the pump inlet fitting
- Blow from the equipment pad outward in this order: pump, filter, heater, return lines
- Hold air at each return until you see bubbles stop in the pool water, then immediately cap the fitting with a plug
- Insert a pool plug or Gizzmo in the skimmer throat after blowing out the skimmer line
If you don’t have a compressor and can’t borrow one, pour non-toxic RV antifreeze into the lines as a backup. Use only RV-rated (non-toxic) antifreeze, never automotive antifreeze, which is toxic and will contaminate your pool water.
Refer to certified pool operator recommendations{:target=“_blank”} for standard blowout pressure guidelines.
Step 6: remove and store equipment
Before covering, strip down everything removable:
- Ladders and handrails: Remove, rinse, and store indoors or in a garage. Metal corrodes under a wet cover over winter.
- Return fittings and eyeball jets: Remove from return ports; install winterizing plugs in each opening.
- Skimmer basket: Remove the basket; install a Gizzmo or rubber plug in the skimmer throat.
- Pump motor: In hard freeze climates, remove the motor and store it in a dry indoor location. Prolonged moisture causes bearing corrosion.
- Automation or controllers: Disconnect and store any controllers not rated for outdoor winter temperatures.
Step 7: install the winter cover
Add the winter algaecide (polyquat 60 type) and drop in the slow-release floater before the cover goes on. We recommend polyquat 60-type algaecide as the standard choice for winter closing. Avoid copper-based algaecides, which can stain pool surfaces over the winter months.
Cover type comparison:
| Type | Cost | Best For | Maintenance Required |
|---|---|---|---|
| Solid tarp | $30-$200 | Budget pools, algae prevention | Must pump standing water off top |
| Mesh safety cover | $300-$900 | Households with children or pets | Rain drains through; check tension monthly |
| Solid safety cover | $600-$1,500 | Maximum protection and safety | No water accumulation; most durable |
Anchor method depends on your deck: drill anchors into concrete, or use water bags on pavers or around an above-ground pool perimeter. The cover should have zero slack, a loose cover traps debris underneath and can collapse into the pool.
For how to deal with standing water on solid covers through the winter, see removing standing water from your pool cover.
Above ground vs. inground: key differences
| Step | Above Ground | Inground |
|---|---|---|
| Water level | Drain completely (portable pools) or lower 4-6 inches | Lower 4-6 inches below skimmer only |
| Plumbing blowout | Usually simpler, fewer lines to blow | More complex, main drain plus multiple returns |
| Pump motor | Remove and store indoors | Store motor indoors in hard freeze climates |
| Cover type | Cover specific to pool shape | Safety cover with deck anchors |
| Antifreeze | Optional if full blowout done | More critical due to longer pipe runs |
See the pool closing checklist by climate zone{:target=“_blank”} for freeze-depth data by region, useful for knowing how aggressive your blowout needs to be.
How much does pool closing cost?
DIY winterization costs $50-$150 in chemicals and supplies. If you already have the cover and equipment from previous years, the recurring chemical cost is the lower end of that range.
Professional closing services charge $150-$400 depending on region, pool size, and what’s included. We found the main advantage of professional closing is that technicians carry proper air compressors and specialized plugs for every fitting type, making the blowout more thorough.
For a full breakdown of professional vs. DIY cost factors, see what professionals charge to close a pool.
DIY pool winterization costs $50-$150 in chemicals and supplies; professional closing services charge $150-$400 depending on region and pool size.
When you’re ready for spring, reverse the process with our guide on how to open your pool in spring.
FAQ
When should I close my pool?
Close when water temperature consistently stays below 65°F. Closing too early (warm water) lets algae grow under the cover. Closing too late (after hard freezes) risks damage to any plumbing still holding water. Most seasonal climates hit the 65°F trigger between late September and early November.
Can I skip blowing out the plumbing lines?
No. Water trapped in plumbing lines expands when it freezes and cracks pipes, fittings, and equipment. Repair bills of $500-$2,000 are common for skipped blowouts. If you lack the tools, hire a professional for this one step only.
What’s the best winter pool cover?
A solid safety cover is the best option if budget allows, it provides security for children and pets, requires no pumping, and lasts 10-15 years. Solid tarps work if cost is the constraint, but you’ll need a cover pump to remove standing water after rain. Mesh safety covers are a middle ground but let some light through, which can encourage algae growth in mild climates.
How long does it take to winterize a pool?
Most DIY closings take 2-4 hours from start to cover installation. Chemistry balancing should happen one week earlier. Day-of tasks include shocking the night before, then the equipment and cover work the following morning.
Should I shock before or after adding algaecide?
Always shock the night before closing. Add algaecide the next morning, once FC has dropped below 5 ppm. Chlorine destroys algaecide on contact, adding them together wastes the algaecide.
Can I close a pool myself or do I need a professional?
DIY is practical for most pool owners with this guide and the right supplies. The one exception: the plumbing blowout. If you don’t have an air compressor or shop vac, consider hiring a professional just for that step. Skipping or doing it partially is the most common cause of freeze damage.