Closing your pool for winter is one of the most important things you can do as a pool owner. A proper winterization protects your equipment from freeze damage, prevents algae growth, and makes your spring opening dramatically easier.
Skip winterizing or do it wrong, and you could be looking at cracked pipes, a blown pump, or a swamp-green pool that takes days to recover. The good news is the process takes a few hours and is straightforward once you know the steps.
When Should You Close Your Pool?
Close your pool when water temperature stays consistently below 65 degrees Fahrenheit. In most northern states, that means mid-September to late October. In the South, you may not need to close at all, or you might close in November or December.
Closing too early is worse than closing late. Warm water under a cover with no circulation is a breeding ground for algae. Wait until the temperature drops and stays down.
If you are not sure your water chemistry is ready, grab a reliable kit from our list of best pool test kits and test before you start.
What Happens If You Don’t Winterize?
Skipping winterization is a gamble that almost never pays off. Here is what can go wrong:
- Frozen plumbing lines that crack and cost hundreds or thousands to replace
- Pump and filter damage from water expanding as it freezes inside the housing
- Algae blooms that turn your pool into a green swamp (see our green pool water fix guide)
- Surface staining and scale buildup from unbalanced water sitting for months
- Damaged heaters and chlorinators that were not properly drained
Winterizing Supplies Checklist
Gather everything before you start so you are not running to the pool store mid-process. If you time it right, you can pick up most of these supplies at a discount during end-of-summer pool deals:
- Pool water test kit or test strips
- pH increaser or decreaser, alkalinity increaser, calcium hardness increaser
- Winter algaecide (long-lasting formula) and pool enzyme treatment
- Chlorine shock
- Pool antifreeze (non-toxic, propylene glycol-based)
- Expansion plugs, return line plugs, and skimmer gizmo
- Winter pool cover with clips, water bags, or anchors
- Shop vac or air compressor for blowing out lines
Step-by-Step Pool Winterization
Step 1: Balance Your Water Chemistry
Start by testing and adjusting your water chemistry. You want the following ranges:
- pH: 7.2 to 7.6
- Total alkalinity: 80 to 120 ppm
- Calcium hardness: 175 to 225 ppm
- Chlorine: 1 to 3 ppm
Unbalanced pH corrodes metal fittings and damages surfaces over winter. If your pH is low, our guide on how to raise pH in a pool covers the fix. If chlorine is too high, see our how to lower pool chlorine guide.
Balance the water two to three days before closing so chemicals circulate and stabilize.
Step 2: Deep Clean the Pool
Give the pool a thorough cleaning. You want it as clean as possible before covering for months.
- Skim the surface, brush walls, steps, and floor, and vacuum thoroughly
- Clean out skimmer baskets and the pump strainer basket
- Remove ladders, slides, diving boards, and rail fittings
Anything left in the pool over winter can stain surfaces or breed algae. Take everything out, clean it, dry it, and store it indoors.
Step 3: Shock the Pool
Add a heavy dose of chlorine shock 24 to 48 hours before closing. Use calcium hypochlorite shock at two to three pounds per 10,000 gallons. Run the pump overnight so the chlorine distributes evenly.
Do not add winterizing chemicals at the same time as shock. High chlorine burns off algaecide. Wait until chlorine drops to 1 to 3 ppm before adding winter chemicals.
Step 4: Lower the Water Level
How far you lower the water depends on your cover type:
- Solid covers: 4 to 6 inches below the skimmer opening
- Mesh covers: 12 to 18 inches below the tile line
- Above-ground pools: 1 inch below the skimmer mouth (never drain completely as walls rely on water pressure)
Use a submersible pump or your filter’s waste setting. Never drain the pool entirely. In-ground pools can pop out of the ground from hydrostatic pressure, and above-ground walls can collapse.
Step 5: Drain and Store Equipment
Water left inside equipment will freeze, expand, and crack housings. Drain every piece of equipment connected to your pool:
- Pump: Remove the drain plugs and let it drain completely. Store the plugs in the pump basket so you can find them in spring.
- Filter: For sand filters, set the multiport to winterize and remove the drain plug. For cartridge filters, remove and clean the cartridge and store it inside. For DE filters, backwash, drain, and remove the grids.
- Heater: Drain per the manufacturer’s instructions. Most have drain plugs on the header.
- Chlorinator: Remove remaining tablets and drain completely. Leaving tablets inside over winter damages the housing.
- Salt cell (if applicable): Remove, clean with a mild acid wash, and store indoors.
If your pump has been giving you trouble, now is a good time to diagnose the issue. Check our pool pump troubleshooting guide before spring so you can order parts over the winter.
Step 6: Blow Out the Plumbing Lines
This is the most critical step for preventing freeze damage. You need to force all water out of the underground plumbing lines.
Use a shop vac set to blow or an air compressor (below 25 PSI to avoid damaging pipes) to blow air through each line:
- Blow air back through the skimmer line until you see bubbles in the skimmer, then plug immediately
- Blow each return line until bubbles appear at the wall jet, then plug with a threaded expansion plug
- Blow out the main drain line if accessible
Once you see bubbles at each outlet, plug it right away before water seeps back in. After plugging all lines, pour pool antifreeze into the skimmer and any lines you are unsure about. Use one gallon per line as a safety measure.
Step 7: Add Winterizing Chemicals
With chlorine back to normal levels, add your winter chemicals:
- Winter algaecide: A long-lasting, non-foaming formula that keeps algae from growing in stagnant water all winter.
- Enzyme treatment: Breaks down organic matter like sunscreen, body oils, and leaves that cause staining over the winter.
- Stain and scale preventer (optional): Add this if you have hard water or a history of staining.
Pour chemicals directly into the pool and use a brush to distribute since the pump is already disconnected.
Step 8: Install Plugs and Gizmos
If you have not already plugged the skimmer during the blowout step, install a skimmer gizmo now. A gizmo is a hollow plastic tube that absorbs the pressure of expanding ice so the skimmer does not crack.
Double-check that every return jet has a plug and the main drain is secure. Pools with slides or water features need those lines blown out and plugged too.
Step 9: Install the Winter Cover
The cover is your pool’s primary defense against debris, sunlight, and animals all winter. The type of cover you use matters. For a full breakdown, see our guide on the best pool covers.
For in-ground pools:
- Solid covers block all light and debris but require a cover pump to remove standing water. Place water bags around the perimeter to hold the cover down. Never use bricks or cinder blocks as they can fall in and damage surfaces.
- Mesh safety covers let water pass through, eliminating the need for pumping. They anchor into the deck with brass anchors and springs.
- Automatic covers just need to be closed with tracks cleared of debris.
For above-ground pools:
- Use a cover designed for your pool’s size and shape. Secure it with a cable and winch and cover clips on the top rail.
- Place an air pillow under the cover in the center. This absorbs ice expansion pressure and prevents the cover from sinking under rain and snow weight.
Make sure the cover is tight with no gaps where leaves and debris can blow in. A loose cover defeats the purpose.
Step 10: Winter Maintenance
Winterizing is not entirely set-it-and-forget-it. Check on your pool periodically:
- Remove standing water, leaves, and snow from solid covers with a cover pump or soft broom
- Make sure the cover is secure and water bags have not leaked
- After major storms, inspect for damage
- If you see algae growth through a mesh cover, add more algaecide
Above-Ground vs. In-Ground Winterizing Differences
The process is largely the same, but there are a few key differences for above-ground vs. in-ground pools:
Above-ground pools:
- Keep the water just below the skimmer mouth. Never fully drain as water provides structural support.
- Use an air pillow under the cover to handle ice expansion.
- Disconnect the pump, filter, and hoses and store them indoors since above-ground equipment is more exposed.
- Remove and store the ladder and A-frame supports.
In-ground pools:
- Water level can be lowered further depending on cover type.
- Plumbing blowout is more involved since lines run underground.
- Equipment may need to be partially winterized in place.
- Safety covers with deck anchors are the most common cover choice.
Common Pool Winterizing Mistakes
Avoid these errors that lead to expensive spring repairs:
Closing too early. If the water is still warm, algae will bloom under the cover. Wait until the temperature is consistently below 65 degrees Fahrenheit.
Not lowering the water enough. Water at the skimmer level will freeze and crack the skimmer.
Skipping the plumbing blowout. This is the single most expensive mistake. A cracked underground pipe costs hundreds to thousands to repair.
Adding algaecide and shock at the same time. High chlorine destroys algaecide on contact. Shock first, wait for chlorine to drop, then add algaecide.
Using bricks or rocks to hold down the cover. They fall in, scratch surfaces, and tear liners. Use water bags or proper anchors.
Forgetting to drain the pump and filter. Even one freeze-thaw cycle can crack a pump housing or filter tank.
Not cleaning the pool before covering. Organic debris sitting in closed water for months causes staining and a much harder spring opening.
Leaving the water unbalanced. Low pH corrodes metal fittings. High calcium causes scale. Balance the water even though nobody is swimming.
Frequently Asked Questions
How much does it cost to winterize a pool?
DIY winterizing costs $75 to $200 for chemicals, antifreeze, plugs, and gizmos. A professional pool closing service runs $150 to $400 depending on location and pool size. Either way, it is minimal compared to the thousands you could spend on freeze damage repairs.
Can I close my pool without blowing out the lines?
You can use pool antifreeze as an alternative, but blowing out lines is the preferred method. Antifreeze alone does not guarantee protection in extremely cold climates. The safest approach is to blow the lines and add antifreeze as backup.
How far should I lower the water for winter?
For solid covers, 4 to 6 inches below the skimmer. For mesh safety covers, 12 to 18 inches below the tile line. For above-ground pools, about 1 inch below the skimmer opening. Never drain completely.
Should I run the pool pump during winter?
In regions where temperatures stay above freezing most of the time, you can run the pump on a timer during the coldest hours to prevent freezing. In areas with extended freezes, it is safer to fully winterize and shut everything down.
When should I open my pool in the spring?
Open when temperatures consistently reach 65 to 70 degrees Fahrenheit, typically March through May. Opening earlier prevents algae from gaining a foothold. Our pool opening guide and pool season prep checklist walk you through everything.
Closing Thoughts
Winterizing your pool takes a few hours in the fall and saves you days of headaches and potentially thousands in repairs come spring. Follow each step, do not cut corners on the plumbing blowout, and invest in a quality cover. Your future self will thank you when opening day arrives and the water is clear instead of green.