Closing a backyard pool for winter means balancing and shocking the water, draining the pump and filter, lowering the water level below the skimmer and fitting a proper winter cover before hard freezes set in. Across most of Canada, that window opens once the pool water cools consistently below about 10 C, which typically falls somewhere between mid-September and late October depending on the region. Waiting too long risks a hard freeze cracking pipes, fittings and even the pool wall itself, while closing too early, before the water has cooled enough, can leave the pool more prone to algae blooming under the cover. Doing the steps in the right order, cleaning and balancing first, then draining, then sealing, protects what is often a significant backyard investment and makes reopening the pool next spring far less work.
- Give the pool a final deep clean. Skim floating debris, brush the walls and floor to loosen algae and dirt, and vacuum the bottom. Empty the skimmer and pump baskets. Any debris left to decompose over winter feeds algae and stains the liner or surface.
- Test and balance the water chemistry. Before adding any closing chemicals, get the water into the target range: pH between 7.2 and 7.6, total alkalinity between 80 and 150 parts per million, and calcium hardness between 175 and 275 parts per million, according to Home Depot’s pool-closing guidance. Balanced water resists scaling, corrosion and algae growth over the winter months far better than water that is left too acidic or too hard.
- Shock the water, then add winter algaecide. Apply a pool shock at the dose listed on the product label and run the pump for at least four hours to circulate it fully. Follow with a winter-strength algaecide, then let the pump run roughly 24 hours so it disperses evenly through the water, as recommended in Home Depot’s closing steps. This combination is what keeps the water from turning green under a sealed cover.
- Lower the water level. Drain the pool until the water sits four to six inches below the skimmer opening, a level confirmed by both Home Depot and Ontario-based pool retailer Coastal Pools. Too high and ice expansion can damage the skimmer and tile line; too low and an above-ground liner can lose the support of the water pressing against it, risking strain or collapse.
- Drain and store the equipment. Fully drain the pump, filter and, if applicable, the heater, along with any hoses, following the manufacturer’s instructions for each piece. Coastal Pools and Calgary-based Trevi Pools both stress that any water left in a pump, filter housing or heater core can freeze and crack it. For a sand filter, set the multi-port valve to the winterize position; for a cartridge filter, remove it, rinse it and store it indoors; for a saltwater chlorine generator, switch it to its winterized setting. Where possible, bring smaller components like the pump and hoses indoors for the season.
- Plug the fittings and skimmer. Remove the eyeball return fittings and replace them with the rubber winterizing plugs (or “gizzmos”) made for that purpose, and fit a skimmer guard or plug. On an inground pool with underground plumbing, the lines to the skimmer and returns typically need to be blown clear with compressed air before they’re plugged; if that equipment isn’t something you own or you’re not confident doing it, this is a good task to hand to a local pool service rather than guess, since water trapped in a buried line can crack it.
- Add an air pillow or ice-equalizer. Place a partially inflated pool pillow in the centre of the water, anchored so it stays away from the walls. As surface ice forms and expands, the pillow compresses instead of the ice pushing outward against the pool’s walls or liner.
- Clear the deck. Take out ladders, handrails that unbolt, skimmer baskets, thermometers and any other loose deck accessories, and store them somewhere dry. Left in place, most of this hardware isn’t built to handle a Canadian winter’s freeze-thaw cycles.
- Install a proper winter cover and secure it well. Use a cover designed for winter closing, either a solid safety cover or a heavy-duty winter tarp, rather than a lightweight summer cover or a plain tarp with water bags, which several Canadian pool retailers, including Trevi Pools, caution against for anything but the mildest climates. Pull the cover taut and secure it with the manufacturer’s clips, cables or water bags, adding extra anchoring in regions that see heavy snow load. Check on it after the first big snowfall or windstorm to make sure it’s still snug and hasn’t pooled with water.
Once the cover is on and the equipment is drained and stored, the job is largely done until spring. It’s worth checking the cover periodically through the winter, especially after major storms, to clear off heavy snow and confirm the water level and anchoring still look right. A pool closed carefully in the fall generally needs only a straightforward chemical rebalance and a light cleaning to reopen, while one closed in a hurry, or with warm, unbalanced water left underneath a summer cover, is far more likely to need a costly spring cleanup or repairs.
