How to Shock a Pool

A person doing shocking of his pool using chlorine

Shocking your pool is a fast and easy way to sanitize its water and raise its free chlorine level. It’s especially important to perform after a rainstorm or pool party. But what exactly is pool shock and how does it work? This article will teach you how to shock a pool and answer all your shocking questions, like, how to use liquid and granular shock and the best time to shock. 

What is pool shocking?

Shocking your pool means adding chemicals to the water to raise the free chlorine level to the point where contaminants such as algae, ammonia, chloramines, and bacteria are eliminated. Free chlorine refers to the chlorine molecules that are available to sanitize contaminants.

Pool shock is usually made from calcium hypochlorite, but potassium monopersulfate, sodium dichloro-s-triazinetrione, and sodium hypochlorite are also used.

Simply put, shock is concentrated chlorine.

These pool chemicals are widely available at your local pool and home improvement stores.

Both chlorinated and saltwater pools use chlorine as a way to kill bacteria and sanitize the water. Chlorinated pool owners manually add chlorine to the water to sanitize their pool, while saltwater pools rely on a generator to supply a steady mix of chlorine. You may be “shocked” to learn that saltwater pools require the same amount of free chlorine as traditional chlorine pools!

The proper amount of free chlorine in your pool is between 1.0 and 3.0 parts per million (or 0.00013 ounces of chlorine per gallon of water). You can monitor chlorine levels with a pool water test kit.

Maintaining the right amount of chlorine in your pool is essential because too much chlorine can damage your eyes and skin. In contrast, low chlorine levels can spawn algae, harmful bacteria, and microorganisms.

Why shock your pool?

A person doing Shock pool chlorination
Slobo | Canva Pro | License

There are lots of reasons to shock a pool. Anytime there’s a dip in chlorine levels brought on by heavy use, contamination, heavy rains, or depletion by the sun, shocking your pool can sanitize and rebalance the chlorine levels in your pool water. Incorporating shock treatments into our pool care routine will protect your pool’s surface and equipment.

Remove chloramines

When free chlorine molecules attach to contaminants, they become combined chlorine or chloramines. Since the molecules are preoccupied with contaminants, they can no longer disinfect new ones. By adding pool shock, you burn off the contaminants, allowing the chlorine to become “free” to capture new contaminants.

If your pool has a strong chlorine smell, it’s time for a shock treatment. Why? Because what you are smelling are chloramines. It may seem counterintuitive, but that “pool smell” is a gas byproduct of chlorine and ammonia.

Clean up waste and byproducts 

It’s uncomfortable to imagine, but your pool can quickly become contaminated with heavy use. Sunscreen, makeup, conditioner, sweat (and other bodily fluids) contaminate your pool water with each use. Shocking your pool is the best way to sanitize your water after a busy pool day.

Renew after rainfall 

Every time it rains, your pool is inundated with contaminants. As clouds drop water from local lakes, roads, and the ocean into your pool, you’ll want to erase all that foreign bacteria before your pool becomes a cloudy uninhabitable cesspool. Rainwater also dilutes your pool, so shock is needed to boost chlorine levels back to the normal range.

Remove and prevent algae

Green, yellow, pink, and black algae can all be eliminated with shock. It may take 2 to 4 doses of shock to eliminate your algae, depending on the severity of your problem. 

Pro tip: Do not mix algaecide and pool shock because the mixture renders them useless. 

How to shock a pool

Blue colored Gallons of liquid pool chlorine
Maksym kozlenko | Wikimedia Commons | CC BY-SA 4.0

Before adding the chlorine, go ahead and check your pool’s pH levels. The chlorine will work most effectively when the pH is balanced. The ideal pool water pH is between 7.4 and 7.6. 

The most challenging part of shocking a pool is determining how much shock to add. To calculate the amount of shock to add, you must first test your water to determine your starting chlorine level using a test kit or strip. Test the water at a 1-foot-deep depth to get an accurate sample. Test in hand, dip your arm into the water until the waterline reaches your elbow. 

Once you have your reading, refer to your shock’s dosage instructions to determine how much shock you’ll need per 10,000 gallons. Different shocks come in different strengths, so always follow the instructions. 

You have several options when it comes to shocking your pool: granular chlorine, liquid chlorine, and non-chlorine shock. Let’s take a closer look at the three. 

Granular chlorine

Always read the measurement instructions on the package label when measuring how much granular chlorine you’ll need to shock your pool. After shocking the pool, wait at least 24 hours before swimming in your pool again and ensure the free chlorine level is between 1.0 and 3.0 ppm. 

Mix your shock with 2 to 3 gallons of pool water in a 5-gallon bucket. Read the measurement instructions carefully, as shock is available in different strengths.  

With the pool pump turned on, pour the mixture around the perimeter of your pool. 

If you notice granules accumulating on the bottom of your pool, use your pool brush to sweep the shock back into circulation. Shock can discolor your pool’s lining.

When dealing with chemicals, wearing protective clothing and eyewear is always a good idea.

Liquid chlorine

Liquid sodium hypochlorite, also known as liquid chlorine, is concentrated chlorine similar to bleach, which contains 6% chlorine. Liquid pool chlorine typically contains 12.5% chlorine. 

To use this chlorine, pour it directly into the water after testing. Unlike granular chlorine, this sanitizer doesn’t need to be diluted. Make sure the pump is running when you add anything to your pool.

Liquid chlorine is less expensive than granular chlorine; however, muriatic acid is often needed to correct the pH imbalance due to the liquid chlorine’s high pH.

Take note that liquid chlorine is rarely 100% chlorine. When shocking your pool, always refer to the product’s instructions on recommended dosages. 

Non-chlorine shock

Whereas traditional shock is concentrated chlorine, a non-chlorine shock does not affect your chlorine levels. This shock uses oxygen and potassium as a water sanitizer. It takes about 1 pound of non-chlorine shock to treat a 10,000-gallon pool.

This sanitizer works by oxidizing organic byproducts in your pool, like dead skin cells and leaves. Plus, it clears out the sunscreen, sweat, and dirt. Non-chlorine shock also oxidizes chloramine. This type of shock is great for homeowners looking for a less abrasive sanitizer for lower-traffic pools.

Pros of non-chlorine shock

  • You can swim 15 minutes after using this shock
  • No added Cyanuric acid in the water
  • Won’t increase calcium hardness levels
  • Minimal effect on pool water chemistry
  • Reduces inorganic chloramines
  • Minimal impact on pH and total alkalinity

Cons of non-chlorine shock

  • It doesn’t work on algae
  • Won’t wipe out pathogenic bacteria that cause illnesses
  • Less effective on high-traffic pools

Sprinkle this sanitizer around the deep end of your pool (with the pump running) if your water looks cloudy or smells strongly of chlorine.

FAQ about pool shock

Can I pour shock directly into my skimmer?

No. Adding shock directly to the skimmer can cause a dangerous chemical reaction. The gasses released by the reaction can damage pipes and the automatic chlorinator if applied directly to the skimmer. Stick to mixing your shock in a bucket and pouring it into the deep end around the return jets.

Should I brush the pool before shocking?

If you see algae developing, brush your pool before shocking it. Brushing loosens the algae and tears the algae’s skin, allowing for more effective removal and prevention.
If you don’t have a problem with algae, save the brushing for after you shock. Brushing after you add shock stops the chlorine from gathering at the bottom of your pool, which causes bleaching.

How long should I wait to swim after shocking my pool?

After adding shock, you’ll need to wait 24 hours to use your pool. All that chlorine will dry out your skin and hair. Plus, inhaling the gasses produced by chloramines is harmful to your lungs. Stay safe, wait at least 24 hours, and then test the water again.

When is the best time of day to shock my pool?

The best time of day to shock your swimming pool is in the evening. Since the UV rays deplete chlorine, shocking at dusk allows the free chlorine to sanitize the pool without getting burnt up by the sun.

Need a Pool Pro?

If you don’t have the time to monitor your pool’s water chemistry, you might be interested in hiring a professional to maintain your pool. On average, professional pool maintenance costs about $1,430 per year, with a typical range between $1,065 and $1,800

And what good is a beautiful pool if your lawn looks lackluster? Let a local lawn care expert hook you up with a fresh-cut lawn just in time for your pool party.

Main Image Credit: Isai Hernandez | Canva Pro | License

Caleb Leonard

Caleb Leonard is a freelance writer and marketing professional. A graduate of the University of North Texas, his interests include gardening, podcasts, and studying Spanish.