An Ontario pool sits through four months of freeze-thaw. The goal of winterizing is not to keep the water clean — it is to make sure no water is trapped anywhere it can expand. A pool closed correctly opens in May with clear water and intact plumbing. A pool closed in a hurry opens with a split line and a green swamp.
Do these eight steps in order. Steps 3 to 5 are the ones that cost money if you get them wrong; the rest are about starting next season clean.
The eight-step sequence
- 01
Clean and balance the water
Vacuum and skim, then balance pH to 7.2–7.6 and total alkalinity to 80–120 ppm. Shock the pool and run the pump 24 hours so nothing organic is left to decompose under the cover.
- 02
Lower the water below the skimmer
Use the filter on waste to drop the level 6–12 inches below the skimmer mouth. Never drain a vinyl-liner pool — the liner needs water weight to stay seated.
- 03
Blow the skimmer line
Connect a high-volume blower to the skimmer and run it until only air comes out. Plug the skimmer while air is still escaping so no water can run back.
- 04
Blow and plug each return
Blow the returns one at a time and plug each one immediately. If you plug too early, water stays in the line and freezes.
- 05
Air-lock the main drain
Blow the main drain until bubbling stops at the floor, then close the valve to trap the air lock. This is the step most DIY jobs miss.
- 06
Add non-toxic antifreeze
Use pool-grade propylene glycol in any line that could not be fully cleared and in the skimmer housing. Never automotive antifreeze.
- 07
Drain and protect the equipment
Drain the filter, pump, heater and salt cell. Pull the drain plugs, store the pressure gauge indoors and cover the pad so snow does not sit on the valves.
- 08
Dose, cover and record
Add winter algaecide or chlorine — never both — fit and tension the cover, and photograph the pad and valve positions. Pump standing water off the cover within a week.
What it costs when a line freezes
The blowout exists for one reason: a return line full of water becomes a split return line. Repairs are expensive because the plumbing is under the deck.
| Service | Typical low | Typical high |
|---|---|---|
| Split return line repairDeck cutting and patching | $1,200 | $2,500 |
| Cracked skimmer replacement | $400 | $900 |
| Frozen heater manifold | $1,500 | $3,000 |
| Safety cover replacement | $1,800 | $4,500 |
| Liner damage from draining | $4,500 | $8,500 |
Typical GTA repair costs, before HST. Compare with a $350–$750 professional closing.
Five mistakes that cause real damage
- Plugging before the air clears. Plug while air is still leaving the line, not afterwards. Once you stop blowing, water runs back.
- Skipping the main drain. The main drain holds the most water and is the hardest to reach in spring. Air-lock it and close the valve.
- Draining a vinyl pool to the floor. The liner shrinks and wrinkles. Stop 6–12 inches below the skimmer.
- Mixing winter chemicals. Chlorine and algaecide can react. Add one or the other, not both in the same dose.
- Leaving the cover loose. A slack cover collects water, stretches and becomes a drowning hazard. Tension every spring or anchor.
Mesh cover or solid cover?
Mesh covers let meltwater drain through, so there is less pumping and less standing water. Solid covers block sunlight, which suppresses algae, but need a cover pump and careful tensioning. For a pool surrounded by maples or oaks, a solid cover with a pump is usually the lower-maintenance choice; for a windy open lot, mesh handles snow load better.
Whichever you choose, the cover is a safety device first. A properly anchored cover supports weight; a tarp with water bags does not.
When to call a crew instead
Hire it out if you do not own a blower, if your valve layout is unclear, or if the pool has a heater, salt system or water feature with additional lines. A closing runs $380–$750 in the GTA and includes the blowout, antifreeze and cover install — cheaper than one repair. Compare Toronto, Mississauga and Vaughan closing prices, then check the full checklist.