Guide to Pool Closing Chemicals What chemicals do I need? Close an inground pool Close an above ground pool Close a saltwater pool When to shut your pool?

Guide to Pool Closing Chemicals

When summer fun winds down and fall breezes blow in, it’s time to close the pool. While this chore brings reluctant groans, it’s important to close your pool carefully in order to protect it for the next swim season.

Going through the steps to properly close your pool makes opening it the next spring so much nicer. Instead of opening a pool that resembles a green swamp, you should find clean and clear water that simply needs chemical balancing. Plus, properly winterizing your pool can save you money. By taking cautious steps now, you can avoid expensive repair costs for frozen plumping lines and busted pool equipment.

To learn more about pool closing chemicals, keep reading. We’ll share pool closing information for inground, saltwater, and above ground pools.

swimming pool chemical chart

What chemicals do I need to close my pool?

Many chemicals you need for closing your pool are things you use for regular pool maintenance. Other chemicals needed to close a pool work specifically to keep pool water clean during winter months. After you analyze your pool chemical levels and conditions, you may need to add some or all of these chemicals:

An element in the form of solid calcium hypochlorite tablets or granules or liquid sodium hypochlorite

Why You Need It
  1. Keeps water clean
  2. Destroys harmful bacteria
  3. Keeps algae away
Tips for Usage

Chlorine tablets in a floating dispenser may not work as well in winter when your pump doesn’t run. Try a chlorine pill that time releases chlorine through the winter.

High dose chlorine or non-chlorine potassium peroxymonosulfate sanitizes pool water

Why You Need It
  1. Removes contaminants
  2. Destroys chloramines
  3. Breaks apart harmful bacteria
Tips for Usage

Add chlorine-based pool shock up to a week before closing your pool. Non-chlorine pool shock can be added a few days before closing the pool.

Sodium carbonate (Na2CO3) is a chemical content with an alkaline pH of 11.3-11.7

Why You Need It
  1. Raises pool pH
  2. Raises total alkalinity
  3. Less expensive to use than baking soda
Tips for Usage

Don’t add too much soda ash or it could make your pool water cloudy.

Sodium bicarbonate (NaHCO₃) is a chemical compound with a mildly alkaline pH

Why You Need It
  1. Raises total alkalinity
  2. Raises pH slightly
Tips for Usage

This common baking ingredient helps balance your pool’s pH and total alkalinity.

Muriatic or hydrochloric acid is used to balance total alkalinity and pH of pool water

Why You Need It
  1. Lowers total alkalinity
  2. Lowers pH
Tips for Usage

This acid is too strong for vinyl-lined or fiberglass pools. It can destroy these pool materials.

This chemical prevents and kills algae growth.

Why You Need It
  1. Kills algae
  2. Prevents new algae growth
  3. Releases when temperatures get warm
Tips for Usage

Add to water one day before closing your pool. Winter algaecide lies dormant until temperatures rise in the next spring season.

Chemical that prevents pool plumbing from freezing

Why You Need It
  1. Protects pipes from freezing
  2. Prevents expensive plumbing repairs
Tips for Usage

Either completely blow out pool lines in an inground pool or add antifreeze if you live in a cold climate. Consult a pool professional for help.

These chemicals prevent the buildup of metals and minerals

Why You Need It
  1. Prevents metal build-up
  2. Prevents metal staining
  3. Prevents mineral build-up during winter months
Tips for Usage

Add stain and scale formulas before you disconnect the pool pump. You want the pump to distribute the stain and scale chemicals throughout the pool.

What chemicals are needed to close an inground pool?

Before you start adding pool chemicals for winter closing, you need to figure out the condition of your water. Use a home test kit such as a liquid testing kit or easy-to-use test strips. For a more precise analysis, you can bring a water sample to your local pool store for professional testing.

inground swimming pool with spa

Pool chemical levels should be at these desired levels:

  • pH should be between 7.2 – 7.4
  • Total Alkalinity should range between 80-120 ppm
  • Calcium Hardness should range between 200-400 ppm
  • Free chlorine should range between 1.5-2.5 ppm

After you test your water, add chlorine and acidic or alkaline substances to get chemical levels in the desired range. Before adding winter pool chemicals, be sure to vacuum, remove leaves and debris, and scrub your pool thoroughly in order to assist chemicals in working effectively.

When basic pool chemistry is balanced, you want to shock your pool. You don’t have to spend extra money on stabilized pool shock unless you have an old or flimsy pool cover. A sturdy pool cover will protect the water from sunlight, so unstabilized chlorine works perfectly.

Other pool closing chemicals include optional chemicals for your specific water needs:

  • If you use a copper algaecide or have high-metal content in your tap water, a stain preventer can keep the copper from staining your pool.
  • Pool enzymes are a helpful add-in if you have a mesh cover that allows rain and pollutants into your pool.
  • Add a winter algaecide to prevent your water from turning green over the winter.
above ground swimming pool

What chemicals do you need to close an above ground pool?

To close an above-ground pool, you need many of the same chemicals needed to close an inground pool. Test and balance chemical levels, using chlorine, alkalizers or acids. Keep in mind these differences for above ground pool closing chemicals:

  • Use a non-chlorine pool shock in above ground vinyl pools or plaster pools. The vinyl or plaster can corrode from harsh chlorine pool shock.
  • Clean your pool and prepare to cover for the winter. Remove ladders and rails so that your pool cover fits securely and prevents rain or snow from disturbing your winter pool chemistry.

Pool Closing Supplies

Pool closing supplies can help pool chemicals keep your pool in good shape through the winter. You’ll want to have these things on hand for optimal off-season pool care: a safety cover to keep all unwanted intruders out of your pool, a pool cover pump to remove water from your pool cover, and an inflatable pool bubble to prevent ice from damaging your pool.

What chemicals do you need to close a saltwater pool?

Just like any other pool, you want to test chemicals levels and balance pool chemistry before closing your pool. Also, test and adjust salt levels. You want salt levels at the low end of the normal range because salt could react with contaminants over the winter months, staining your pool.

Use the same winterizing chemical steps as you would use on any inground pool, including shocking the pool and adding algaecide and stain and scale preventers. You can even buy winter pool kits that include all the chemicals you need in a convenient package.

One additional step for saltwater pools is to remove your salt water generator, drain it, clean it using diluted muriatic acid if necessary, and store for the winter.

Closing Time: When to Shut Your Pool for the Season

How do you know when to shut your pool for the season? For most people, the water will become chilly enough to warn you of fall’s approach. Other factors to consider in deciding when to shut your pool include outdoor temperature. When temperatures consistently dip below 65 degrees, you should probably close your pool. Lower temperatures keep algae growth down, so continue cleaning and sanitizing your pool until the thermometer starts to dip.

After going through these steps to protect your pool for the winter, you can enjoy a break from regular pool maintenance. There is usually no need to test the water in a covered pool. Pool closing chemicals should last for at least six months, unless you have additional water accumulating in your pool. A few weeks before you plan to open your pool, pull the cover back and test the water. If chemical levels are out of range, you can shock the pool and add additional algaecide.

Recommended Brands

Ready to winterize your pool?

Find a Store Near You