Pool closing · California
When to Close Your Pool in San Leandro, CA: Deadline, Window & Checklist
Last updated: July 15, 2026 · Model window year: 2026 · dates · checklist · FAQ
Circle October 28 on the San Leandro calendar. Closing earlier traps warm, algae-friendly water under the cover; closing later gambles the plumbing against the first freeze, which the 1991–2020 normals place near December 23. The window opens October 18 — the live widget below shows how this year is actually tracking against it.
San Leandro closing dates at a glance
| Closing window | October 18 – October 28 |
|---|---|
| Close by (deadline) | October 28 |
| First freeze, 50% probability | December 23 |
| Open by (recommended) | May 15 |
| Opening window | May 8 – May 29 |
| 61°F crossing (7-day mean) | May 29 |
| Swim-season length (80°F+ days) | 0 days |
| NOAA normals station | Oakland Metro International Airport · 3.5 mi · 6 ft |
San Leandro 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 San Leandro curve says roughly 57°F by mid-April, 62°F by mid-June, 64°F in mid-August, then back down through 63°F in mid-October. The summer ceiling sits near 65°F, and every window above is just a line drawn on this curve.
The 12-step San Leandro 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
Three or four days before closing, adjust alkalinity and pH into label ranges. Balanced water is gentler on the liner, plaster, and equipment through the long covered months ahead.
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Deep-clean the pool
Skim, brush walls and steps, and vacuum carefully. Any leaves or algae you seal under the cover become spring's chemistry problem, so closing day cleanliness pays twice.
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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
Run the winter kit through moving water: dose each product per its label with the pump on, give it a few hours to distribute, then start the shutdown. Chemistry added to still water stays where it lands.
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Lower the water level
Check the cover manufacturer's spec before touching the hose: solid covers typically want water below the skimmer mouth, mesh often barely lower than normal. Full draining is off the table entirely.
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Blow out the lines and plug returns
Air through every line — skimmer, returns, cleaner — until each blows dry mist, plugging returns while the air still pushes. Nothing else on this list protects as much plumbing per minute.
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Protect the skimmer
Install a skimmer guard bottle (or a plug rated for your skimmer) so ice that forms there crushes the sacrificial piece instead of cracking the skimmer body.
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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 every drain plug on the pump, filter, heater, and chlorinator, and store the plugs in the pump basket so spring reassembly is a one-stop hunt. Move what you can indoors.
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Set the air pillow and cover
Center an inflated air pillow, then fit the cover and secure it with water bags, cable, or straps as designed. The pillow gives ice a place to push besides your walls.
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Shut down the heater carefully
Follow the manufacturer's winterizing sequence for your heater — drain it fully and, for gas units, close the supply valve. Heat exchangers are the most expensive freeze casualty on the pad.
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Stage the cover pump
Solid covers need drainage all winter: set a cover pump or siphon before the first storm, not after. Standing water strains seams and invites a mid-winter emergency.
What to buy before the rush
Every item below sells out somewhere in California every October. Stocking the short list before the rush costs nothing extra and saves the mid-project store run — the chemicals guide explains what each category actually does.
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Pool antifreeze
Pool-rated glycol for the lines air couldn't clear.
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Winter closing kit
The under-the-cover chemistry, measured for your gallons.
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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.
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Cover pump
Standing water is a cover killer; this is the counter.
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Expansion plugs + skimmer guard
Seals blown-out lines and sacrifices itself to skimmer ice.
How San Leandro compares locally
San Leandro closes in the latest quarter of California's calendar. Neighbors run close: Castro Valley (5 mi away) models its deadline at November 7 (about a week later vs San Leandro's October 28), while Oakland (7 mi) shows November 11. The spring mirror of this page is the San Leandro opening guide, and the season overview draws both windows on a single bar.
Every number on this page traces to one instrument cluster: Oakland Metro International Airport, 3.5 miles west of San Leandro's center at an elevation near 6 feet. NOAA computed its 1991–2020 normals from roughly three decades of daily readings — long enough that one strange spring in Alameda County barely moves the dates.
Field notes for San Leandro owners
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.
The skimmer is the most breakable part you own
Skimmer bodies crack because water freezes inside the throat with nowhere to push. A sacrificial bottle or spring-loaded guard absorbs that expansion for a few dollars. It's the highest-return item in the entire closing kit relative to what it protects.
Cold water is the whole point
A pool closed at 55°F barely changes all winter: algae are dormant, chemicals hold, and spring opens with a light dusting instead of a bloom. A pool closed at 72°F runs its own quiet ecosystem under the cover for a month. The date matters less than the water temperature it represents.
Hard-winter homework
Where winter is long — San Leandro 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.
San Leandro pool closing FAQ
What temperature should water be to close a pool?
Close once water holds below about 65°F — the point where algae go mostly dormant — and before hard freezes. In San Leandro, the 7-day mean drops through the threshold around October 18, so the window between then and October 28 is the sweet spot for a clean, stable close.
Can you close a pool too early?
Yes — it's the most common closing mistake. Seal 70°F water under a cover and algae keep growing in the dark all autumn; the spring opening turns green and expensive. In San Leandro, hold off until the cool-down near October 18 before covering.
Do I need antifreeze in pool lines?
Only where water might remain. If every line is properly blown out and plugged, air is the antifreeze. Lines you can't verify dry — long runs, low spots, water features — get pool-grade antifreeze dosed per its label. With San Leandro's first freeze normal near December 23, don't leave that question open.
How far should I drain my pool for winter?
Follow the cover's instructions first: solid covers usually want water a few inches below the skimmer; some mesh setups run higher with the skimmer sealed. The hard rule is never empty — hydrostatic pressure can lift or crack an empty pool, a far worse outcome than any freeze.
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 San Leandro 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 San Leandro?
The model draws the line at October 28 for San Leandro. It isn't arbitrary: the cool-down plus ten days (the freeze normal, December 23, leaves room to spare), and the whole closing sequence needs a working weekend of margin. The one exception that overrides any date — a hard freeze inside the 10-day forecast, which the widget above flags as urgent.
Email me when San Leandro hits the closing window
Data: NOAA 1991–2020 climate normals via Oakland Metro International Airport (3.5 mi); live outlook by Open-Meteo. Full attribution on the sources page. Model assumptions and error bars on methodology.