Spring Pool Opening: When & How to Open Your Pool in Ontario

Spring in Ontario means one thing for pool owners: it is almost time to take the cover off. But timing matters more than most people realize. Open too early and you are fighting cold water chemistry. Open too late and algae has already started growing under the cover.

This guide covers everything you need to know about opening your pool in Ontario, whether you hire someone or do it yourself.

When should you open your pool in Ontario?

The best time to open your pool is when daytime temperatures are consistently reaching 15°C or higher, and the water temperature underneath the cover stays above 10°C. For most of Southwestern Ontario, that window falls between late April and mid-May.

You do not need to wait until it is warm enough to swim. The goal is to get the water circulating and treated before algae has a chance to grow. Once the water warms up under a dark winter cover with no circulation and no sanitizer, algae can take hold quickly.

Here is a general timeline for Ontario pool openings by region:

Region	Typical Opening Window
Southwestern Ontario (London, Windsor)	Late April to mid-May
Greater Toronto Area	Early to mid-May
Ottawa / Eastern Ontario	Mid to late May
Northern Ontario	Late May to early June

In the London area specifically, most pool openings happen in the first two weeks of May. Some years it is a bit earlier, some years a bit later. Weather varies, so watch the forecast and your water temperature rather than picking a date on the calendar months in advance.

What happens if you open too early or too late?

Opening too early

If you open your pool in early April when temperatures are still dipping below freezing at night, you are not gaining much. The water is too cold for algae to grow aggressively, but it is also too cold for your sanitizer to work efficiently. Chlorine works best in warmer water. You will burn through chemicals without much benefit.

There is also the issue of freeze risk. If you have reconnected your plumbing and a hard frost hits, you could crack a pipe or damage a fitting. That is an avoidable repair.

Opening too late

This is the bigger problem. Once the water under your cover warms past 15°C with no circulation and no sanitizer, algae starts growing. If you wait until June, you may pull the cover off to find green or murky water that takes days of heavy shocking and filtration to clear.

A late opening does not just cost time. It costs money in extra chemicals and frustration.

The rule of thumb is simple: it is better to open a week too early than a week too late.

What should you check before opening your pool?

Before you pull the cover off, take a few minutes to inspect things. Catching problems now is easier than discovering them after the pool is full and running.

• Winter cover condition. Look for tears, holes, or heavy debris loads. If the cover has standing water on top, pump it off before removing the cover. Dumping dirty rainwater into your pool makes the opening process harder.
• Water level. Check the water level through the skimmer or by lifting a corner of the cover. The water should be at normal operating level, about halfway up the skimmer opening. If it is low, the pool may have a slow leak or the water simply evaporated over winter.
• Visible equipment. Walk around the pool pad and look at the pump, filter, heater, and plumbing. Check for cracked pipes, loose fittings, or any signs of frost damage. Look for rodent nests in the equipment area.
• Deck and coping. Check for any cracked or shifted patio stones, loose coping, or trip hazards that developed over the winter freeze-thaw cycle.
• Fence and gate. Make sure your pool fence is intact and the self-closing gate latches properly. This is a safety requirement, not optional.

What is the step-by-step pool opening process?

Here is the general process for opening an inground fiberglass pool in Ontario. The exact steps may vary slightly depending on your equipment, but this covers the main sequence.

Step 1: Remove the winter cover

Pump off any standing water from the top of the cover first. Then carefully remove the cover, pulling it toward one side of the pool. Try not to let debris fall into the water. Have a second person help if the cover is heavy.

Once the cover is off, clean it, let it dry completely, fold it, and store it somewhere dry. A wet cover stored in a shed will grow mould over the summer.

Step 2: Remove winterizing plugs and accessories

Pull out the winterizing plugs from the return jets and skimmer. Remove the Gizzmo (the plastic skimmer protector) if you used one. Take out any pool noodles or air pillows that were floating under the cover.

Step 3: Reinstall accessories

Put the skimmer basket, return jet eyeballs, ladder, handrails, and any other accessories back in place. Check the ladder bolts and handrail anchors. They can loosen over winter.

Step 4: Reconnect the equipment

Open the valves on the pump, filter, and heater. Reinstall any drain plugs you removed from the pump and filter during winterizing. If you have a sand or DE filter, check the multiport valve and make sure it is set to "Filter." If you have a cartridge filter, make sure the cartridge is clean and properly seated.

Step 5: Top up the water

Fill the pool to normal operating level, about halfway up the skimmer opening. Use a garden hose. This can take several hours depending on how low the water dropped.

Step 6: Prime and start the pump

Fill the pump basket with water to help prime it. Turn on the pump and let it run. You may need to bleed air from the filter by loosening the air relief valve on top until water starts coming out. Once you have steady flow and no air in the lines, you are circulating.

Step 7: Clean the pool

Skim any floating debris. Vacuum the bottom if there is sediment. Brush the walls and floor. The fiberglass gel coat is smooth, so a soft-bristle brush is all you need. Do not use steel brushes on fiberglass.

Step 8: Test and balance the water

Test the water for pH, alkalinity, chlorine, and calcium hardness. Then adjust as needed. We cover this in more detail in the next section.

Step 9: Shock the pool

Add a strong dose of chlorine shock to kill any bacteria or early-stage algae. Follow the product directions based on your pool volume. Run the pump for at least 24 hours after shocking.

How do you get the water chemistry right at opening?

After months of sitting dormant, your pool water will be out of balance. That is normal. The goal at opening is to get the basics back in range and shock the water to sanitize it.

Here are the target ranges you are aiming for:

Parameter	Target Range	Why It Matters
pH	7.2 – 7.6	Keeps chlorine effective and water comfortable
Total alkalinity	80 – 120 ppm	Stabilizes pH and prevents large swings
Free chlorine	1 – 3 ppm (after shock settles)	Sanitizes the water
Calcium hardness	200 – 400 ppm	Protects surfaces from etching or scaling
Cyanuric acid (stabilizer)	30 – 50 ppm	Protects chlorine from UV breakdown

Always adjust alkalinity first, then pH, then everything else. Alkalinity acts as a buffer for pH. If you try to fix pH without getting alkalinity right first, the pH will keep drifting.

The easiest approach is to bring a water sample to your local pool supply store. They will run a full analysis and give you a list of exactly what to add and how much. Most stores do this for free.

For a more complete breakdown of pool water chemistry, see our Pool Water Chemistry 101 guide.

Should you hire a professional or do it yourself?

Both options work fine. The choice comes down to your comfort level with the equipment, your physical ability to handle the cover, and how much your time is worth.

When hiring makes sense

• It is your first spring with a new pool and you have never done an opening before
• You have a safety cover that requires special hardware and tools to remove
• Your pool has automation or complex equipment you are not familiar with
• You would rather spend a Saturday doing something else
• You want a trained eye to spot potential equipment problems

When DIY makes sense

• You have opened the pool before and are comfortable with the process
• Your equipment is straightforward (pump, filter, chlorinator)
• You enjoy maintaining your own pool
• You want to save $250 to $400

If you are new to pool ownership, having a professional handle the first opening while you watch and learn is a reasonable approach. After that, most homeowners can handle it themselves.

How much does a professional pool opening cost?

In Ontario, a professional pool opening typically costs between $250 and $400 CAD. The price depends on the size of the pool, the type of cover, the complexity of the equipment, and whether chemicals are included.

Service	Typical Cost (CAD)
Basic pool opening (tarp cover)	$250 – $325
Pool opening (safety cover)	$300 – $400
Opening chemicals (if not included)	$50 – $100
Water testing and balancing	Often included

Most pool service companies book their spring openings weeks in advance. If you want a specific date in early May, booking in March or April is a good idea. Waiting until the last minute usually means you are pushed to the back of the schedule.

What does a professional opening include?

A standard professional pool opening typically includes:

• Removing the winter cover and folding it (some companies clean it, some do not)
• Removing winterizing plugs and Gizzmos
• Reinstalling the ladder, handrails, and skimmer baskets
• Reconnecting the pump, filter, and heater
• Priming and starting the pump
• A basic water test and initial chemical treatment
• Checking equipment for obvious problems

What is usually not included: deep vacuuming, full water balancing (beyond initial shock), equipment repairs, and cover cleaning. Ask your service provider what is and is not covered before booking.

What should you do during the first week after opening?

The first week after opening is the most important period for getting your water dialled in. Here is what to focus on:

• Run the pump 24/7 for the first 48 to 72 hours. This circulates the shock treatment and filters out debris. After the initial period, you can drop to 8 to 12 hours per day.
• Test the water daily. pH and chlorine can swing significantly in the first few days. Test each morning and adjust as needed.
• Brush the walls and floor. Even on fiberglass, brushing helps distribute chemicals and prevents any algae from getting a foothold on the surface.
• Clean the skimmer basket and pump basket frequently. Spring brings pollen, seeds, and debris that clog baskets fast.
• Backwash or clean the filter. Your filter will catch a lot of fine particles in the first few days. Clean it after 48 hours and again after a week.

After the first week, the water should be clear and the chemistry stable. At that point, you can settle into a normal weekly maintenance routine.

Are there fiberglass-specific considerations for pool opening?

Fiberglass pools are generally easier to open than concrete or vinyl liner pools. A few things to keep in mind:

• Use a soft-bristle brush only. Stiff nylon or steel brushes can scratch the gel coat. A standard pool brush with soft bristles is all you need on fiberglass.
• Check the gel coat. Look for any cracks, chips, or blistering that may have developed over the winter. Small cosmetic issues are normal and can be addressed later. Structural problems (cracking at fittings, separation at the coping) should be looked at by a professional before you fill and run the pool.
• Watch calcium hardness levels. Fiberglass pools do best with calcium hardness between 200 and 400 ppm. Water that is too soft (low calcium) can pull minerals from the gel coat surface over time. Water that is too hard can leave scale deposits.
• Avoid high-copper algaecides. Copper-based algaecides can stain the gel coat surface of a fiberglass pool. If you use an algaecide, choose a copper-free formula.

The smooth gel coat surface of a fiberglass pool resists algae better than concrete, so opening day is usually less work. You are less likely to find a pool full of green water under the cover compared to a concrete pool.

What are the most common pool opening mistakes?

After decades of opening pools, here are the mistakes we see most often:

• Dumping the cover water into the pool. The dirty, stagnant water sitting on top of your winter cover should be pumped off and drained away from the pool, not tipped into the pool. It is full of debris, tannins, and bacteria.
• Skipping the water test. Adding chemicals based on a guess is wasteful and can cause problems. Test first, then add what is actually needed.
• Running the pump without priming it. A dry pump can burn out the seal in minutes. Always fill the pump basket with water before turning it on.
• Shocking the pool with the cover still on. Chlorine shock needs to circulate and off-gas. Adding shock under a closed cover traps chlorine gas and can damage the cover and the pool surface.
• Ignoring the filter. A dirty or clogged filter cannot clean the water no matter how much chemical you add. Start with a clean filter.
• Waiting until June. The single most common mistake. The pool sits warm and stagnant under the cover for weeks longer than it should. Open on time, even if you are not planning to swim until July.

Ontario pool opening timeline by region

If you are planning ahead, here is a general month-by-month timeline for pool opening preparation in Ontario:

Month	What to Do
March	Book your professional opening if hiring one. Order supplies (shock, test kit, pH adjusters).
Early April	Inspect the pool area, fence, and equipment visually. Pump standing water off the cover.
Late April	Check water temperature. If consistently above 10°C and no hard freezes in the forecast, you can open.
Early to mid-May	Most common opening window for London and Southwestern Ontario.
First week after opening	Run pump 24/7, test daily, brush, clean filter, shock as needed.

Planning ahead, especially booking your opening appointment early, avoids the spring rush when every pool service company in the region is booked solid.

Frequently Asked Questions