Pool closing · California
When to Close Your Pool in Seaside, CA: Deadline, Window & Checklist
Last updated: July 15, 2026 · Model window year: 2026 · dates · checklist · FAQ
In Seaside, the closing window runs from October 10 to October 20. Let the water cool out of the algae-growth range before covering — close too warm and you lift the cover onto a green surprise in spring — but finish ahead of the first freeze, which normals place around December 23. The live estimate below shows where Seaside's water sits today.
Seaside closing dates at a glance
| Closing window | October 10 – October 20 |
|---|---|
| Close by (deadline) | October 20 |
| First freeze, 50% probability | December 23 |
| Open by (recommended) | June 17 |
| Opening window | June 10 – July 1 |
| 61°F crossing (7-day mean) | July 1 |
| Swim-season length (80°F+ days) | 0 days |
| NOAA normals station | Monterey Peninsul Airport · 2.7 mi · 165 ft |
Seaside banks only about 0 days of 80°F-plus afternoons — early opening weeks are the cheapest season extension available.
Put dates aside and follow the water: the Seaside curve says roughly 55°F by mid-April, 60°F by mid-June, 62°F in mid-August, then back down through 61°F in mid-October. The summer ceiling sits near 63°F, and every window above is just a line drawn on this curve.
The 12-step Seaside winterizing checklist
A closing is a plumbing project with a chemistry warm-up. Start a few days ahead of your target date, keep every dose per its product label, and don't skip the photographs — spring-you reassembles from them.
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Balance the water a few days ahead
Give the chemistry a head start — balance to label ranges several days out, while circulation can still mix corrections evenly. Closing-day dosing never distributes as well.
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Deep-clean the pool
Brush, skim, and vacuum like company's coming. A pool that goes under the cover spotless comes out needing a rinse; one that goes under dirty comes out needing a project.
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Service the filter one last time
Send the filter into winter clean: backwash the sand or DE, rinse and dry the cartridges indoors. Media stored dirty over winter hardens into a spring problem no backwash fixes.
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Apply winter chemicals per label
Winter chemicals go in before shutdown, not after: label-dosed, circulated for a few hours, distributed evenly. A floater dropped on still water protects one corner.
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Lower the water level
Take the level down only as far as the cover's manual says — usually just below the skimmer for solid covers, higher for many mesh systems. An empty pool is never the goal; shells crack and shift without water's weight.
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Blow out the lines and plug returns
Push air through skimmer, return, and cleaner lines until they run dry mist, then seat expansion plugs at each return while air still flows. This is the single most important freeze-protection step.
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Protect the skimmer
Give the skimmer something cheap to break: a guard bottle or rated plug absorbs the ice expansion that would otherwise split the housing.
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Add pool antifreeze where blowouts fall short
Antifreeze is the insurance policy for doubtful lines, not a replacement for the blowout: pool-grade product, label dosing, and only where air couldn't finish the job.
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Drain the equipment
Open the drains on everything that holds water and let the pad empty completely. Cartridges and small equipment overwinter far better on a garage shelf than outside.
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Set the air pillow and cover
Inflate the pillow to about two-thirds, center it, then bring the cover over and secure it per its design. Under ice, that soft dome is the difference between inward compression and outward wall pressure.
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Calendar the off-season checks
Set a monthly reminder from October 20 to spring: check cover tension, pump off standing water, and glance at the water level. Fifteen minutes a month protects the whole closing job.
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Note this year's dates
Jot down when Seaside's water actually cooled and when you closed. A two-line note beats memory next October 10 — your own yard runs a few days off any model, including ours.
What to buy before the rush
The October crowd empties shelves in a predictable order. This is the short list worth owning before Seaside's window opens — nothing exotic, just the stuff everyone needs the same weekend.
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Cover pump
Solid covers collect rain all winter; this is the drainage plan.
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Expansion plugs + skimmer guard
The blowout's finishing move — one per return, one for the skimmer.
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Pool antifreeze
Pool-rated glycol for the lines air couldn't clear.
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Winter closing kit
Season-length winter chemicals in one label-dosed box.
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Air pillow
Centers under the cover so ice pushes inward, not outward.
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Winter cover
The one purchase every other closing step depends on.
How Seaside compares locally
Two nearby data points to triangulate with: Salinas, 11 miles from Seaside, models its close at October 31 (roughly two weeks later); Watsonville, 21 miles out, at October 28. Seaside's own window ends October 20. For the other half of the calendar see when to open in Seaside, or scan the full year on the season page.
The measuring stick here is Monterey Peninsul Airport — 2.7 miles to the southwest, elevation about 165 feet. Its 1991–2020 record is what the model reads for Seaside; your backyard in Monterey County will run a touch warmer or cooler with shade, wind, and pavement, which is exactly the slack the two-week lead absorbs.
Field notes for Seaside owners
Cover pumps die in the cold — plan for it
A cover pump left running into a hard freeze can lock in ice and burn out. On freezing forecasts, pull it, let the storm pass, and put it back for the melt. Automatic models with freeze protection earn their price in exactly one forgotten weekend.
The warm spell after you closed
A 78°F week in October doesn't mean reopening. Water under an opaque cover warms far less than air suggests, and a closed, balanced pool tolerates a warm stretch fine. Check the cover pump has somewhere to send rain, enjoy the weather, and leave the plumbing sealed.
Match the drainage plan to the cover
Solid covers shed nothing — they need a cover pump staged before the first storm and checked after each one. Mesh covers drain themselves but pass silt that settles all winter. Either way, the plan is decided in October, not improvised in January when the cover is an ice sheet.
Hard-winter homework
Where winter is long — Seaside banks only about 0 warm-swim days — the closing carries months of load. Bury the effort where it counts: verified-dry lines, fully drained equipment, a skimmer guard, and a cover secured for real wind. A short season forgives a late opening; it never forgives a cracked pump.
Seaside pool closing FAQ
What temperature should water be to close a pool?
Below roughly 65°F, and trending down. Water closed warm keeps feeding algae under the cover for weeks; water closed in the 50s goes dormant almost immediately. Seaside's cool-down lands near October 10 in the normals, which is why the window opens there.
Can you close a pool too early?
Absolutely. A pool closed warm is an algae incubator: no circulation, fading sanitizer, and weeks of growth-friendly temperatures. Seaside's water doesn't settle below the risk zone until around October 10 — closing much before that trades a few weekends of maintenance for a rough spring.
Do I need antifreeze in pool lines?
Blown-out, plugged lines don't need it; doubtful lines do. Use only antifreeze labeled for pools, at the label's rate per foot of pipe — never automotive antifreeze. In Seaside the freeze clock starts around December 23, so settle this during closing, not during the first cold snap.
How far should I drain my pool for winter?
As far as your cover manufacturer specifies and no farther — typically a few inches below the skimmer mouth for solid covers, near normal level for many mesh systems with skimmer plugs. Never drain fully: an empty shell can shift or crack under groundwater pressure.
What happens if you don't winterize a pool?
The repair list writes itself in order of cost: heater heat exchanger, pump housing, filter tank, then every fitting the ice reached — discovered one leak at a time in spring. Around Seaside the exposure begins near December 23, and each skipped checklist step above is one more candidate for that list.
When is the last safe date to close in Seaside?
Treat October 20 as the deadline in Seaside. It's derived from the 1991–2020 normals: the cool-down plus ten days (the freeze normal, December 23, leaves room to spare). Weather varies year to year, so watch the 10-day forecast in late October — an early cold snap moves the real deadline, and the widget above flags exactly that.
Email me when Seaside hits the closing window
Data: NOAA 1991–2020 climate normals via Monterey Peninsul Airport (2.7 mi); live outlook by Open-Meteo. Full attribution on the sources page. Model assumptions and error bars on methodology.