How to Winterize a Pool in 12 Steps

Adjust Phosphate Levels One Week Prior

Phosphate acts as an all-you-can-eat buffet for algae, and you’ll need to carefully balance your phosphate levels so you don’t end up with a green pool come spring. About a week before you close your pool, add a phosphate remover. Sometimes this product is wrapped into an algaecide, so always check the labels. You don’t want to accidentally double up on products. 

Instructions vary, but you can generally pour the recommended amount into the skimmer while the pump is running.

Remove and Clean Pool Accessories

When the day arrives to close down your pool for the season, start by removing and cleaning any accessories in your pool, such as ladders, skimmer baskets, cleaners, floats, solar blankets, and steps. Gently wash off any dirty accessories and let them dry before storing them away in a safe location.

Deep Clean Your Pool

Hopefully, you’ve kept on top of pool cleaning duties throughout the swimming season. That way, winterizing your above ground pool won’t be too arduous a task. You can add scale and stain remover a couple of weeks before you start the job.

1. Gently scrub the sides and base of the pool with a pool brush and get everything off the floor (use a pool vacuum if you have one). 

2. Use a leaf brush or skimmer net and be meticulous about lifting debris from the water surface. 

3. The cleaner you leave the pool, the less chance of algae building during the winter.

Add Stain and Scale Prevention Products

Stains and scale can build up on the walls of your pool while it’s not in use—and they’re a pain to remove once they latch on. To prevent this, add a stain and scale prevention product (though balancing your calcium levels should help a great deal).

Stain and scale inhibitors are included in most inground or above ground pool winterizing kits. Add the product per the manufacturer’s instructions. Typically, you’ll need to pour in the proper dose when your pump is running. The pump helps circulate it through the water.

Test and Adjust the Water Chemistry

Using your testing kit, check the pool water chemistry (chlorine, alkalinity, pH) and adjust as appropriate. You can use baking soda to raise the pH and alkalinity or calcium chloride to increase the calcium hardness. Aim for the following:

• Alkalinity concentration between 80–120 parts-per-million (ppm) 

• pH level between 7.3–7.6

• Calcium hardness between 175–225 ppm (for a vinyl or fiberglass liner)

• Chlorine (if you use this for cleaning) between 1–3 ppm

• Plumping for the higher end of the ranges means the chemical balance lasts better through the winter.

Add Shock and Algaecide

Shocking your pool sounds dramatic, but it's simply the name given to the process of adding a specific chlorine or non-chlorine chemical pool product to raise the free chlorine level. This helps get rid of pesky chloramines, bacteria, algae, and other contaminants that make your pool cloudy and unsanitary.

You should already be familiar with the process, as it's done regularly throughout the summer as part of ongoing pool maintenance. But it’s also an essential step in winterizing your above ground pool.

Always follow the manufacturer guidelines for application and dosage volumes. For a very dirty pool, you might have to shock it two or three times to maintain safe chlorine levels. If you're concerned about algal growth, you can also add an algaecide, but check whether it's safe to use this alongside your shock treatment.

Alternatively, lift the cover of your pool every few weeks during winter and if you see any signs of algae growth, add the algaecide then.

Clean Your Pool Filter

You want to kick off winter with a squeaky clean pool filter, especially if you’re storing your filter indoors. The method depends on the type.

Diatomaceous Earth (DE) Filters

Let your pump run for at least eight hours, then drain your filter. Remove the grids, and give them a thorough rinse with a garden hose. Once you’ve removed the excess DE, leave the valves open.

Cartridge Filters 

Let your pump run for at least eight hours, then drain the filter. Remove the filter cartridge, and manually clean it with a hose. Leave the valves open, and store the cartridge indoors in a safe place.

Sand Filters

Sand filters are a bit more complicated. Make sure the filter’s multiport valve is set to “winterize.” After that, you’ll need to remove the drain plug and drain the filter completely. Some sand filters have a bleeder valve and a sight glass, which you’ll also need to remove. You can store these in the pump basket for the season.

Ideally, you’ll want to bring your sand filter indoors for the winter. This isn’t always feasible because sand is heavy. If you can’t lift the filter and plan to leave it outside, make sure you’ve removed the drain plug to prevent cracking.

Add Winterizing Chemicals

After your levels are balanced and you’ve shocked your pool, it’s time to add the final winterizing chemicals. If you’ve purchased a pool winterization kit, it will typically come with a product called a winter pill, winter floater, or winter sorb. These products float on top of the remaining water, releasing a number of chemicals that clarify water, inhibit stains and scale, and enhance helpful enzymes throughout the season. Add the products per the manufacturer’s instructions.

Turn off Your Pool Equipment

When you’ve cleaned your pool and added the right chemicals, it’s time to officially let it hibernate. Turn off your pool equipment—including everything from your pool heater and pump to pool lights and any other equipment. Shut off the main power breaker for your pool, and make sure to deactivate any timers you might have set during the swim season. 

Protect Your Skimmer

An above ground pool skimmer hangs on the side of the pool, just submerged in the water. It pulls water through the basket, filtering off dirt and debris. If you invest in a winter skimmer plate, remove the hose, drain the skimmer, and fit the plate. This prevents freezing and cracking without you having to change the water levels.  

Don’t want to invest in the skimmer plate? Lower the water levels using a hand siphon or pump to 4 to 6 inches below the skimmer. Just don’t drain your pool fully. This dries out the vinyl liner, decreasing its lifespan.

Drain and Store or Cover Equipment

Water in the lines, pumps, or filters continually freezes and thaws during a hard winter. This expansion can damage the equipment. To avoid this and unsanitary mold growth, drain away the water, thoroughly dry the items, and then store them in a dry spot. In particular, you’ll want to remove and store your:

• Pump

• Chlorinator

• Hoses

• Drain plugs and/or caps

• Filters or filter cartridges 

Whatever equipment you can’t store, you’ll need to cover. You can purchase a pool heater cover to protect your heat pump or pool heater. It’s also a good idea to use mothballs and mint sachets to keep pests like mice out of the pool heater when it’s not in use.

Lower Water Level to Install an Air Pillow

When ice or snow builds up on top of your pool cover, it presses against the water and gets stuck when it freezes over. Using an air pillow in the middle of the water surface, or a few if you have a large pool, prevents ice from expanding outwards. You’re less likely to have ice creating damaging pressure on the pool walls. 

Before placing an air pillow on your pool, you’ll need to lower the water levels. This process could take one or two days, depending on the amount of water you need to remove. 

Cover the Pool

You don't want your pool to fill up with leaf litter and other debris over the winter, so fitting a snug, secure cover is a must.

A well-fitting pool cover (steer clear of flappy tarps) stays on regardless of the weather, so don't weigh it down with something like a brick. This is more likely to damage the cover and possibly even the pool. After a big dump of snow, take the time to clear any piles off the cover.