How to Winterize Your Pool the Right Way
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By: Al Cardi
Hey everyone, it’s Al!
Fall is right around the corner, and if you’re like most pool owners I talk to, you’re probably wondering when and how to wrap up the season without causing expensive damage to your setup. Winterizing can feel like a headache, but getting it right is the single best thing you can do to protect your investment and make next spring's opening a breeze. Let's walk through everything you need to know to get your pool closed down properly before the cold weather hits.
Why Most Pool Owners Get Winterization Wrong
Here’s the deal: taking a couple of hours to do a $200 DIY pool closing can save you from a $5,000+ repair bill caused by freeze damage in the spring. We’ve seen it happen more times than I can count on Long Island through our service team at Sapphire Swimming Pools.
Yet, every single fall, I see pool owners get winterization wrong because they’re following bad advice.
The biggest myth out there? That you should close your pool on Labor Day or some random calendar date. The real trigger isn't the month on the calendar—it's water temperature consistently staying below 65°F. Close too early while the water is still warm, and you’re basically building an algae incubator under your cover. Close too late, and you’re gambling with frozen pipes and cracked equipment.
Proper seasonal care prevents up to 75% of spring opening headaches. Here are my personal, step-by-step guidelines for winterizing your pool like the pros do it.
Step 1: Watch the Water Temperature, Not the Calendar
That magic number is 65°F. When your pool water consistently stays below 65°F, it's time to start the closing process. I always recommend checking with a reliable digital thermometer for 3 to 5 consecutive days before picking your close date—one chilly morning doesn't mean it's go-time.
Why is this so critical? Warm water trapped under a dark pool cover creates the ultimate playground for algae. Pull that cover off in May and you'll be staring at a swamp.
On the flip side, waiting too long is just as dangerous. Standard PVC pool plumbing can crack when exposed to sustained temperatures below 28°F, and replacing an underground return line can easily cost between $400 and $1,200.
- Northern States: You’ll be doing a "hard close"—meaning a full plumbing blowout and complete equipment shutdown.
- Sunbelt States (Texas, Arizona, etc.): You likely only need a "soft close" with partial winterization and reduced filtration hours.
Step 2: Balance Your Water Chemistry (The Week Before Closing)
Unbalanced water chemistry is the single most common DIY mistake I see. Water that sits stagnant for 5 or 6 months with improper chemistry will leave heavy scale deposits on your surfaces or corrode your equipment.
Here are the target numbers I aim for when closing:
- pH: 7.2 – 7.6
- Alkalinity: 80 – 120 ppm
- Calcium Hardness: 200 – 400 ppm
- Chlorine: 1 – 3 ppm
Al's Pro Tip: Don't Skip Phosphate Removal
Phosphates above 300 ppb serve as an all-you-can-eat buffet for algae all winter long. Dosing a quality phosphate remover right before closing cuts off that food source completely. We do this on every single closing job at Sapphire Swimming Pools, and it’s the secret behind coming back to crystal-clear water in the spring.
Important: Never close a pool with active algae! Algae spores survive cold weather and will explode the second things warm up. If your water is cloudy or green, shock it and get it clear before you even think about putting the cover on.
Once you add your winterizing chemicals, run your pump for 8 to 12 hours to circulate everything thoroughly. Never put your cover on within an hour of adding heavy chemicals, or you risk bleaching and ruining your vinyl liner! Treat chemistry as a project for the week before your physical closing day.
Step 3: Lower Water Levels & Blow Out the Lines
For in-ground pools, lower the water level 4 to 6 inches below the skimmer line. This protects your skimmer body—one of the most vulnerable and costly parts to replace after a hard freeze.
Al's Golden Rule: NEVER drain your pool completely. Hydrostatic pressure from groundwater can literally pop a fiberglass or vinyl pool right out of the ground, or crack a concrete pool shell.
Next, use a heavy-duty shop vac or air compressor to blow out all standing water from your return and skimmer lines. Once the lines are bubbling clear, add pool antifreeze (propylene glycol) as extra insurance. It lowers the freezing point inside the pipes down to -50°F.
- Never use automotive antifreeze (ethylene glycol)—it’s non-potable, toxic, and will ruin your pool!
Finish up by screwing in reliable winterizing rubber plugs or threaded plugs with Teflon tape into all returns and skimmer ports. Spending $20 on pool antifreeze and plugs is cheap insurance compared to a $2,000 plumbing repair bill.
Step 4: Winterize Equipment (Pump, Filter, Heater & Salt Cell)
Any piece of equipment holding trapped water will freeze, expand, and crack. Freeze damage to a pump or filter housing runs $500 to $2,000 to replace, so take your time here.
- Filter & Multiport Valve: Drain the tank completely. Set your multiport valve setting to "Winterize" (or leave the handle positioned between two settings). Leaving it on "Filter" or "Backwash" seals water inside the valve body and splits it open during a freeze. Unthread and store your pressure gauge indoors—it's a small part people constantly forget, only to find it broken in spring.
- Heater: Pull the drain plugs on the heat exchanger and pressure switch. A cracked heat exchanger costs up to $4,000 to fix, so make sure every drop of water drains out.
- Salt Chlorinators: Turn off your salt system when water temperatures drop below 60°F. Operating the cell in cold water damages the delicate sensor plates. Before freezing temps hit, remove the cell, give it a quick acid wash, and store it inside your garage or basement for the winter.
(I always recommend installing a dummy cell or pass-through pipe over the winter to keep your plumbing aligned and protected.)
Step 5: Secure the Cover
- In-Ground Pools: Secure a solid safety cover or high-density mesh cover using anchor bolts or heavy-duty water bags. Make sure there are zero gaps along the edges where leaves and dirt can blow in.
- Above-Ground Pools: Inflate a pool air pillow to about 60% capacity (do not over-inflate!) and anchor it in the center of the water before pulling the cover over. The pillow acts as an ice equalizer, absorbing expansion pressure so your pool walls don't buckle. Secure the outer edges tightly using a winch and cable system.
If you’re using a solid cover, set up an automatic cover pump to remove rain and snowmelt. Heavy standing water on top of a cover can cause it to collapse straight into the pool.
Al’s Mid-Winter Check
Closing your pool doesn't mean ignoring it until April! A quick 10-minute check every few weeks protects your hard work:
- After heavy wind or winter storms, clear off excess debris and inspect the cover for tears.
- Keep an eye on water levels under the cover—a sudden drop usually signals a slow tear or plumbing leak.
- For above-ground pools, clear excessive snow buildup off the cover so the extra weight doesn't damage the side walls.
Close It Right, Open It Easy
What you put into closing your pool directly dictates how much time and money you'll spend opening it next spring.
By waiting for 65°F water, balancing your chemistry, blowing out your plumbing, and storing your equipment properly, you'll save hundreds in professional fees and prevent thousands in freeze damage.
If you need closing chemicals, blowers, winter plugs, or dummy cells, check out our hand-picked winterization collection at Al's Cool Pool Store. Every product we stock is gear we personally use on job sites every day.
Have questions about your specific setup? Reach out to our team anytime—we’re always happy to help!