Pool Closing Checklist for Ontario Homeowners: Everything You Need to Know

Closing your pool properly at the end of the season is one of the most important things you can do to protect your investment. A proper winterization prevents freeze damage to plumbing, extends the life of your equipment, and makes your spring opening much easier. A poor closing can mean cracked pipes, a damaged pump, or a pool full of algae waiting for you in May.

This checklist covers everything that needs to happen before your pool is sealed up for the Ontario winter.

When to Close Your Pool in Ontario

The standard recommendation for Ontario is to close your pool when water temperatures drop below 18°C consistently. For most GTA homeowners, this happens between late September and mid-October.

Cities closer to Lake Ontario (Toronto, Mississauga, Pickering, Ajax) tend to stay slightly warmer into fall, while northern GTA cities (Aurora, King City, Newmarket) cool down a week or two earlier.

Closing while the water is still warm — above 18°C — increases the chance of algae growth under the cover over winter. Waiting until after the first hard frost risks freeze damage to equipment you have not yet winterized.

The Complete Pool Closing Checklist

Water Chemistry (2 to 3 Days Before Closing)

• Test and balance pH to 7.2–7.6
• Test and balance alkalinity to 80–120 ppm
• Test and balance calcium hardness to 200–400 ppm
• Shock the pool with a high dose of chlorine or non-chlorine shock
• Add a winterizing algaecide
• Allow 48 hours for chemicals to circulate before closing

Equipment and Plumbing

• Backwash and clean the filter thoroughly
• Blow out all return lines with a compressor to remove standing water
• Plug all return inlets and skimmer openings with winter plugs
• Add antifreeze to skimmer lines (do not use automotive antifreeze — use pool-rated antifreeze only)
• Remove and store the pump basket, drain plugs, and pressure gauge
• Drain the pump, filter, heater, and chlorinator completely
• Disconnect and store the pump motor in a dry location if possible
• Remove and store the salt cell from your salt chlorine generator

Pool and Deck

• Lower the water level 15–30 cm below the skimmer (for mesh covers) or to the bottom of the skimmer (for solid covers)
• Remove and clean ladders, handrails, diving boards, and slides. Store indoors if possible.
• Clean the pool walls and floor thoroughly before covering
• Remove all pool toys, floats, and accessories
• Install the winter safety cover and secure all anchors, water bags, or cable system

Common Mistakes That Cause Expensive Problems

Not blowing out the lines. Standing water left in return lines will freeze and expand, cracking PVC fittings and return inlets. This is one of the most common and preventable causes of spring repair bills.

Closing the pool too warm. Warm water plus darkness plus a cover equals an algae bloom. You will open in May to green, unusable water and a significant chemical cost to recover.

Using the wrong antifreeze. Automotive antifreeze is toxic and will contaminate your water. Only use RV or pool-rated propylene glycol antifreeze in pool plumbing.

Skipping the shock treatment. Pre-closing shock kills remaining bacteria and algae and gives you a clean starting point for the winter chemical balance.

Professional Pool Closing in Toronto and the GTA

CA Pool handles closings for homeowners across Toronto, Mississauga, Vaughan, Markham, Brampton, Richmond Hill, Aurora, King City, Ajax, and Pickering. Our closing service covers all of the steps above, starting from $400.

We typically close pools from late September through mid-October. Booking in August or early September ensures you get a date that fits the ideal timing for your pool.