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What’s the Best Pool Shock for Your Swimming Pool?

By Matt Giovanisci | Updated: April 19, 2022

Shocking your pool is part of regular pool maintenance. It helps keep algae, bacteria, and other contaminants from building up in your water. But getting the right kind of pool shock is critical for keeping your water clean and clear.

Not all pool shock products are right for every type of pool or for every pool situation. In general, we recommend the following pool shock:

Want more help picking out the best pool shock for your pool? Here’s a breakdown of how pool shock works, the different types of pool shock, and when to use each one.

How Does Pool Shock Work?

When you shock your pool, you’re adding enough chemicals (usually chlorine) to clean the water and remove the chloramine buildup. These chloramines build up when chlorine mixes with urine, sweat, the oils in our skin, and nitrogen. It’s a naturally occurring chemical process that happens when your chlorine does its job. But it’s what gives a pool that chlorine-like smell.

If you’ve ever visited a hotel pool or to the gym for a quick workout and smelled lots of chlorine, you’ve actually come across an improperly sanitized pool. That strong chlorine odor is a result of the buildup of chloramines in the water, not an indication that the pool itself is clean.

What Are The Best Types of Pool Shock?

Cal-Hypo Chlorine Shock

Calcium hypochlorite shock, or cal-hypo shock, is the most powerful shock treatment for both regular pool maintenance and problematic pool water.

Found usually in granule form, cal-hypo shock is readily available, affordably priced, and straightforward to use. Some versions can be broadcasted directly into your water or you may be required to pre-dissolve it before adding it to your pool.

You can find varieties that contain anywhere from 65% to 75% chlorine. However, it will affect your other chemical levels. Because cal-hypo contains calcium, it can cause scaling and calcium build-up. And it will also raise your water’s pH levels, so if the pH is high after shocking, you’ll need to balance it. However, it is unstabilized chlorine, meaning it does not contain cyanuric acid and it won’t increase your CYA levels.

Cal-hypo shock should only be used at night because it’s unstabilized chlorine and the sun’s UV rays can burn away. Simply add the pool shock to your water at dusk, circulate your water and check your pool the next day.

Dealing with algae or green pool water? Cal-hypo is the best shock treatment for you. It’s powerful enough to kill contaminants and stop algae growth (similar to an algaecide). However, it may require multiple doses, depending on your situation.

It’s a powerful weekly treatment for your pool, especially if you deal with ongoing green water or cloudy water. However, it’s not suitable for saltwater pools, hot tubs, or even smaller-sized pools. Always follow the manufacturer’s instructions and pay attention to the guide on the package.

Dichlor Shock

Also known as sodium dichloro-s-triazinetrione or sodium sichlor, dichlor shock can be used for both shock treatments and regular chlorine doses.

Unlike cal-shock, it contains only 50% to 60% chlorine and is made with stabilized chlorine so it won’t burn off in the sun.
But that means it will add 0.9 ppm of cyanuric acid for every ppm of additional free chlorine. So avoid using this kind of pool shock if your water test kit shows higher than normal cyanuric acid levels.

Most brands can be added directly to your pool, but a few must be dissolved first. And after adding it to your pool water, you’ll need to wait 8 hours before swimming again.

You can also find lower percentage dichlor products (15% to 20%) that work as “shock-and-swim” options. These typically let you swim about 15 minutes after treating your pool, but you should always read the label and follow the instructions.

Non-Chlorine Shock

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If you want to shock your pool and swim soon after, a non-chlorine shock is your best option. Opting for this potassium mono sulfate shock gives you a gentler pool shock alternative without affecting your other chemistry levels.

You can add non-chlorine shock to your pool water anytime day or night. And since it’s both fast-acting and gentle, you can safely swim again after about 20 minutes. This is also a great option for smaller, above ground pools since traditional chlorine shock takes longer to dissipate.

Looking to kill the algae in your pool? Unfortunately, a non-chlorine shock isn’t powerful enough to eliminate green water and algae growth. And this type will only work if there’s a chlorination system present within the pool. This is the preferred way to shock a saltwater pool or a hot tub.

By the way, if you need more help keeping your pool clean and clear, check out our pool maintenance video course.

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The Pool Care Handbook

What to Consider When Choosing Your Pool Shock

Saltwater vs. Traditional Pool

The difference between a traditional pool and a saltwater pool is simple: you’re adding salt to one and adding chlorine to the other. But a saltwater pool and chlorine pool both contain chlorine. That’s because the salt in a saltwater pool is converted into chlorine by a salt-chlorine generator.

Because of this, adding a high-chlorine shock to your pool could easily over-chlorinate your water and throw off the chemical balance. And cal-hypo shock is notorious for causing scale build-up in saltwater pools.

That’s why it’s best to use either dichlor shock or non-chlorine shock for regular saltwater pool maintenance and cal-hypo shock for algae issues. Even saltwater pools need to be shocked every week or two (and more often if there’s been heavy rain or high usage). But if your saltwater generator has a “super chlorinate” option, you can use that to increase the chlorine in the water which would effectively shock your pool.

Granule vs. Liquid vs. Tablet Shock

Pool shock is available in several forms: granule, liquid, and tablet.

Stabilized vs. Unstabilized Shock

Unstabilized shock doesn’t have cyanuric acid added to it. Pool shock with CYA stabilizes the chlorine to make it last longer in the pool and in the sunlight. Without the added acid, the UV rays break down the chlorine, making it less effective.

If you want to shock your pool without affecting your CYA levels, use shock without added cyanuric acid (like cal-hypo shock). Just be sure to shock it at night when the sun won’t burn up the unstabilized chlorine.

How Much Chlorine You Need

For a regular weekly pool shock, you might not need a high concentration of chlorine. However higher chlorine levels are necessary for treating green water, problematic pools, or sanitizing after lots of swimmers have been present.

Each type of pool shock has different levels of chlorine:

pH Levels

Chlorine-based pool shock will always alter the pH level of your pool. But non-chlorine shock won’t.

Check the pH level after you add the shock and check it again before getting into the pool to make sure your pH level has returned to normal.

Your pool’s ideal pH level should be anywhere between 7.4 to 7.6, with 7.5 being ideal. If the pH level is too high, the water is too basic, or alkaline. This can lead to eye irritation – swollen, itchy, red eyes are nobody’s idea of fun. When the pH falls too low, the water becomes too acidic which leads to skin irritation – itching, burning, and rash.

If you need help balancing your pH levels, check out our guide to Basic Pool Chemistry 101.

Dissolving Time

When using a liquid pool shock, you won’t need to worry about dissolution time. But, if you opt for a tablet or a powder treatment, you should consider the dissolving time when you plan to shock your pool.

Powders are quick-dissolving. But they may require premixing to prevent damage to vinyl pool liners. Tablets, on the other hand, take the longest to completely dissolve.

Never swim while the tablet is dissolving and follow all of the manufacturer’s directions about swim time. And after you shock your pool, check the pH balance to make sure the water is safe before diving in.

Algae Problems

Even pool owners who take excellent care of their pool water deal with algae issues. And some shocks are better than others at clearing up your water.

Cal-hypo shock is an effective way to handle algae growth and destroy organic contaminants. But how much you use depends on what kind of algae you’re up against.

Frequently Asked Questions about Pool Shock

Have more questions about picking out the right pool shock for your swimming pool? Here are some common questions and answers.

What is the best pool shock treatment?

The most effective pool shock treatment depends on your pool’s condition and the type of pool you have. Our top pick for the most powerful pool shock is cal-hypo shock. But non-chlorine shock is the most gentle and won’t affect your other chemistry levels.

What type of shock should I use in my pool?

The type of pool shock you should use depends on the type of pool you have and why you’re shocking your pool. If you’re dealing with algae or a build-up of organic contaminants, use cal-hypo shock. If you’re shocking as part of regular pool maintenance, it’s fine to use any type of shock. Just know that dichlor shock will raise your cyanuric acid levels. And if you have a saltwater pool, the best shock treatment is with either a dichlor shock or a non-chlorine shock. You can use cal-hypo shock for algae issues, but it can raise your calcium levels.

Is pool shock all the same?

No, in fact, there are three main types of pool shock – calcium hypochlorite, sodium dichloro-s-triazinetrione, and potassium monopersulfate. Each one is used for a different reason and in different pools.

What is the difference between shock and super shock for pools?

The difference between these two kinds of pool shock comes down to the concentration of calcium hypochlorite. A super shock treatment is more concentrated than the standard version.

Is liquid chlorine better than pool shock?

Pool shock and liquid chlorine are chemically the same but they have extremely different concentrations of chlorine. You will need to add significantly more liquid chlorine than you would cal-hypo shock if you want to oxidize chloramines in your pool.

Are pool shock and chlorine the same thing?

No, they are similar but aren’t the same thing. Shock has a much higher concentration of chlorine compared to chlorine sanitizers.

How often should you shock your pool?

Shock your pool once a week during the pool season to help keep algae at bay and kickstart your sanitizer. If you have a rainstorm or lots of people using your pool, shocking more often may be necessary.

Can I over shock my pool?

Adding too much shock can disrupt the chemical balance in your pool water. You may notice cloudy water and you won’t be able to use your pool before it clears up. If you’re still having issues with cloudy water after a few days, consider using a pool clarifier or pool flocculant.

Occasionally adding too much shock won’t be an issue, but do it too often and you risk damaging your pool equipment or your vinyl liner. Pool shock impacts your pH levels. And low pH can cause pool equipment corrosion. If it’s too high, scale may build up on your equipment and pool walls.

Can I use bleach in my pool?

While bleach does contain the active ingredient chlorine, it’s in a lesser concentration than in most pool shock products. It’s not recommended to use bleach in place of a shock. If you add bleach, you risk damaging your pool and causing health issues, especially if you’re using other pool chemicals to balance your pool water chemistry.

Need More Pool Maintenance Help?

Matt Giovanisci is the founder of Swim University® and has been in the pool and spa industry since 1995. Since then, his mission is to make pool and hot tub care easy for everyone. And each year, he continues to help more people with water chemistry, cleaning, and troubleshooting.
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