Pool closing · California
When to Close Your Pool in Fontana, CA: Deadline, Window & Checklist
Last updated: July 15, 2026 · Model window year: 2026 · dates · checklist · FAQ
In Fontana, the closing window runs from November 18 to November 28. 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 30. The live estimate below shows where Fontana's water sits today.
Fontana closing dates at a glance
| Closing window | November 18 – November 28 |
|---|---|
| Close by (deadline) | November 28 |
| First freeze, 50% probability | December 30 |
| Open by (recommended) | March 11 |
| Opening window | March 4 – March 25 |
| 61°F crossing (7-day mean) | March 25 |
| Swim-season length (80°F+ days) | 164 days |
| NOAA normals station | Ontario International Airport · 8.5 mi · 949 ft |
Fontana's 164-day warm season leaves comfortable margins on both ends — the windows above aim you at the cheap-chemistry versions of each transition.
Put dates aside and follow the water: the Fontana curve says roughly 63°F by mid-April, 72°F by mid-June, 80°F in mid-August, then back down through 72°F in mid-October. The summer ceiling sits near 80°F, and every window above is just a line drawn on this curve.
The 12-step Fontana winterizing checklist
Sequenced against Fontana's November 18–November 28 window: chemistry while the pump still runs, blowouts before the equipment drains, cover last. Labels dictate every dose.
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Balance the water a few days ahead
Start midweek for a weekend close: bring alkalinity and pH into their label ranges and let the water settle. What you seal under the cover is what the pool soaks in until spring.
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Deep-clean the pool
Make the last cleaning the best one of the year: full skim, full brush, careful vacuum. Debris left behind steeps all winter and greets you as April's water problem.
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Service the filter one last time
Backwash sand or DE, or pull and rinse cartridges, per the manual. A filter stored dirty cakes over winter and starts spring half-clogged.
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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
Drop the level as your cover manufacturer specifies — typically below the skimmer mouth for solid covers. Never drain a pool fully; groundwater pressure can damage the shell.
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Blow out the lines and plug returns
Work line by line: push air until the return spits dry mist, plug it against the flowing air, move on. Skimmer, returns, cleaner line, in whatever order your plumbing prefers — dry pipes are the entire point of closing.
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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
Nothing on the pad should hold water overnight: pull the drain plugs from pump, filter, heater, and feeder, stash them all in the pump basket, and carry the portable pieces indoors.
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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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Remove and store ladders and rails
Pull ladders, rails, and the diving-board hardware; rinse, dry, and store them out of the weather. Anchor sockets get a dab of protectant so spring bolts turn freely.
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Calendar the off-season checks
Set a monthly reminder from November 28 to spring: check cover tension, pump off standing water, and glance at the water level. Fifteen minutes a month protects the whole closing job.
What to buy before the rush
Every item below sells out somewhere in California every November. 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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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
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
Measure with overlap; the winter workhorse over everything else.
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Cover pump
Solid covers collect rain all winter; this is the drainage plan.
How Fontana compares locally
Two nearby data points to triangulate with: Rialto, 4 miles from Fontana, models its close at November 28 (the same day); Rancho Cucamonga, 6 miles out, at November 28. Fontana's own window ends November 28. For the other half of the calendar see when to open in Fontana, or scan the full year on the season page.
Local means local: Fontana's dates come from Ontario International Airport, the nearest station with complete daily temperature normals — 8.5 miles west, about 949 feet up. Between that station and a San Bernardino County backyard there's always a degree or two of microclimate; the windows are built wide enough to carry it.
Field notes for Fontana owners
The fifteen-minute monthly walk-around
Once a month all winter: pump or siphon standing water off solid covers, re-tension straps or top up water bags, confirm the level hasn't dropped enough to strand the cover, and glance at the pad for critter nests. Every major cover failure starts as a skipped walk-around.
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 mesh-cover spring surprise, prevented in fall
Mesh-covered pools green up early because late-winter sun plus nutrient-carrying meltwater reaches the water. The fall counter-moves: close late and cold, dose the winter kit exactly per label, and plan an early-spring peek under the cover rather than a Memorial Day reveal.
Fontana pool closing FAQ
What temperature should water be to close a pool?
Cold enough that biology has clocked out — below 65°F and falling, ideally low 60s. The widget above tracks Fontana's actual water; the normals say the durable cool-down arrives near November 18, and anything inside the window to November 28 closes clean.
Can you close a pool too early?
Early closing is the mistake the whole model is built to prevent from the other direction. A cover installed over 70°F water is a terrarium: sanitizer decays, algae compound, nobody looks for months. Fontana's water isn't reliably out of that zone until about November 18 — the calendar's first cold weekend doesn't change that.
Do I need antifreeze in pool lines?
Only for lines you can't verify dry — a proper blowout makes antifreeze unnecessary. Where doubt remains, use pool-grade product at its label rate, never automotive. No freeze-probability normal is published near Fontana, so let the live forecast, not a calendar, tell you when freeze protection starts mattering.
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?
In a freeze climate, physics wins: water expands about 9% when it freezes, cracking pump housings, filter tanks, heat exchangers, and pipes. With Fontana's first 32°F night arriving near December 30 in the normals, an unwinterized pad is a spring repair bill waiting to be discovered.
When is the last safe date to close in Fontana?
November 28, by our model — the cool-down plus ten days (the freeze normal, December 30, leaves room to spare). Later closes happen, but they happen in gloves. The winterizing steps above take a weekend; leave yourself at least that much runway before Fontana's first freeze-risk stretch.
Email me when Fontana hits the closing window
Data: NOAA 1991–2020 climate normals via Ontario International Airport (8.5 mi); live outlook by Open-Meteo. Full attribution on the sources page. Model assumptions and error bars on methodology.