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Shocking your pool on a regular basis is a simple way to prevent stray algae and bacteria from taking root in your water. It also helps keep your pool smelling … well, hopefully like nothing at all.
This is the ultimate guide to keeping your pool sparkling clean throughout the year that contains everything you need to know about taking care of your pool the right way.
Pool shock is a chemical that oxidizes chloramines in your pool water. “Shocking” your pool is also a process called superchlorination. By shocking your pool, you’re adding enough chlorine (or another chemical) to sanitize the water and destroy the buildup of chloramines.
Chloramines form when chlorine mixes with the nitrogen in sweat, oils, and urine. This is a natural chemical process, basically a byproduct of your chlorine doing its job.
Think back to the last time you walked past a hotel pool. The strong chlorine smell actually comes from chloramines, a sign of improperly sanitized water.
Shocking your pool can also help clear up cloudy water and kill pool algae growth if your pool is green.
Before we dive into how to shock a pool, you first have to understand the difference between total and free chlorine, and combined chlorine and breakpoint chlorination.
Try to reach the breakpoint every time you shock your pool. Not hitting the breakpoint can result in even more chloramines in your pool, and if the chloramine levels continue to rise unchecked, you may eventually have to partially or even fully replace your water to fix the issue.
If you want to learn more about the difference between free and combined chlorine, we wrote a full article about it here.
You generally can’t shock your pool using regular chlorine tablets, but you do have your choice of products when it comes to pumping up your chlorine levels.
Also known as cal hypo, this chemical has been used to disinfect swimming pools and municipal water sources since 1928. It’s one of the most inexpensive and convenient ways to shock your pool.
This fast-acting, quick-dissolving swimming pool shock kills bacteria, controls algae, and destroys organic contaminants in pools.
If your water has high calcium content, and you don’t mind paying a little extra, lithium hypochlorite is the way to go. It dissolves much more quickly than calcium hypochlorite, so you can add it directly to your pool without dissolving it beforehand.
Note: You may have a difficult time finding lithium hypochlorite. Some pool chemical manufacturers have stopped producing it due to the rising cost of lithium, most of which is now used to make lithium batteries.
The actual names of this swimming pool shock chlorine are sodium dichloro-s-triazinetrione or dichloroisocyanuric acid. (Try saying either of those five times fast.) Dichlor shock is much easier to say and even easier to use. Depending on the brand, you may be able to add it directly to your pool. Also, you can use this type of shock for saltwater pools.
This multifunctional pool shock from Clorox comes in a 12-pack. The algae-fighting granules create crystal clear water by killing bacteria and organic contaminants. It works well for smaller pools and saltwater pools. As a dichlor-based stabilized cholorine shock, it does contain cyanuric acid.
If you’re looking to shock your pool and take a dip soon afterward, this is exactly what you need. Non-chlorine shock using potassium peroxymonosulfate is a fast, inexpensive pool shock alternative. This is the preferred shock for saltwater pools.
A powerful oxidizing agent that eliminates combined non-sanitizing chlorine (chloramines) and provides higher free chlorine levels. Helps eliminate algae growth as well as harmful bacteria. Ideal for use with chlorine or bromine sanitized applications, weekly maintenance, and will not affect other chemical levels
The instructions on chlorine shocks say they need to be used after the sun has gone down. This is because the sun’s uv rays burn off unstabilized chlorine, which means the shock won’t be as effective. Shocking your pool at night makes sure the chemicals work the way they were meant to.
We recommend shocking your pool once a week, or at least once every other week, to maintain sanitized water chemistry properly. The more often you use the pool, the more often you should reach for the swimming pool shock. In addition to your weekly or semi-weekly treatments, you may want to perform an extra pool shock under certain circumstances, such as after:
Think of extra shocks as insurance against wayward algae and other contaminants. It’s better to take out any bacteria before it has a chance to affect the quality of your water or make anyone sick.
Superchlorinating your pool is shockingly easy (sorry, we couldn’t resist) once you get the hang of it. Also, this process works for any type of swimming pool, including inground, above-ground, and small inflatable or quick-set pools.
Important: Remember, if you’re using chlorinated pool shock, wait until the sun goes down before adding it.
Before you start, you’ll need to calculate your pool’s volume. If you don’t already know how much water your pool holds, you can use this pool calculator to figure it out.
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Do a quick round of pool water testing. The Free Chlorine level should be lower than the Total Chlorine level. This means your Combined Chlorine level is off and it’s time to shock your pool.
Also, check the pH and alkalinity levels. Make sure your pH level is between 7.4 – 7.6 and your alkalinity level is between 100 and 150 parts per million (ppm). This will balance the pool water chemistry so the shock treatment is more effective.
You can also check your calcium hardness level to make sure it’s in balance with the pH and Alkalinity. If your pool has a vinyl or fiberglass liner, the calcium hardness level should be between 175 parts per million (ppm) and 225 ppm. If you have a concrete or plaster pool, keep the level between 200 ppm and 275 ppm.
Carefully read the manufacturer’s instructions on your shock product. Most packages include charts or steps to help you calculate the amount of shock you need. If you need to calculate it yourself.
If you need to dissolve the shock first, fill your bucket roughly ¾ full with warm water. Add the shock to the bucket, and slowly stir until the chemical is as dissolved as possible. Work in one-pound increments.
If you do not need to dissolve your shock, count how many containers of shock you need. Add one bag at a time until you reach your calculated breakpoint.
At this point, make sure your pool pump and pool filter are running at full speed. This will help mix in the shock more effectively. Keep the system running for at least 8-12 hours after adding shock.
Slowly pour the shock while walking around your pool for more even distribution. (If your shock-water mix has solid particles at the bottom, dip the bucket into your pool water, carefully swish around to dissolve, and keep pouring.)
Wait to use your pool based on when you added the shock and the manufacturer’s recommendations. You don’t want to irritate your skin and eyes or bleach your swimsuit.
Is it okay to shock a saltwater pool? A lot of pool owners think saltwater pools are different from traditional chlorine pools. But the salt in the water passes through a generator which turns it into chlorine. All saltwater pools are actually chlorine pools. The only benefit is that you don’t have to add the chlorine yourself. It’s being generated by your filter system.
This means you can shock your pool using the traditional shock methods outlined in this article. However, we recommend only using Dichlor or non-chlorine shock for saltwater pools.
You don’t always have to shock the pool this way. Most saltwater generators include a “super chlorinate” button that ramps up the production of the chlorine it produces helping you get to breakpoint chlorination, thereby “shocking” your pool.
And just like a traditional pool, we recommend doing this one a week or every two weeks depending on weather and usage. For heavy rain and/or high usage, shock your saltwater pool once a week.
Shocking your pool is a necessary part of good maintenance, but please remember those chemicals can be extremely dangerous if they’re mishandled. We’re not exaggerating the danger—improperly stored chlorine can literally explode.
Looking for more help with shocking your pool? Here are some common questions and answers.
No. There are versions of shock that have chlorine, like Calcium Hypochlorite. But some pool shock treatments have no chlorine. However, you can use a high dose of liquid or granular chlorine to shock your pool.
We recommend running your pump and filter when you’re actively shocking your pool and for at least 8-12 hours after. If you don’t run your pump and circulate the water, you run the risk of bleaching your pool walls and floor if you’re using chlorine shock.
It’s usually safe to swim after letting the shock circulate in the water for at least 8 hours. However, we recommend testing the water’s chlorine level before swimming. A high chlorine reading may be uncomfortable and dangerous to swimmers.
Yes, but no matter what the temperature of your pool water, we recommend dissolving shock in a bucket of warm water before adding it. This will help dissolve the shock so it doesn’t sit on the bottom of your pool and cause bleaching. Plus, it helps it to mix into the water better and faster.
Matt is the founder of Swim University. He's been in the pool industry since 1993. His mission is to make pool care easy for everyone. Each year, he continues to help more people with water chemistry, cleaning, and troubleshooting.
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