Is Hot Tub Shock and Chlorine the Same Thing?

measuring chlorine pollution in blue water of outdoor pool by chemical tester

The different chemicals needed to maintain a hot tub can be a bit confusing. Many new hot tub owners have wondered: is hot tub shock and chlorine the same thing?

Here’s what I know from owning 4 hot tubs for over 15 years:

Hot tub shock and chlorine are not the same thing. There is chlorine-based shock, but not all shock products are chlorine-based. Hot tub sanitizer can be either chlorine or bromine. Sanitizer is added a few times per week to sanitize the water, whereas shock is added weekly to reactivate the sanitizer.

Shock help enhance the sanitizing power of chlorine or bromine and reactivate the chloramines or bromamines that sanitizer turns into eventually.

What we’ve just learned is just the tip of the iceberg. There’s a lot more info that’ll help you keep your hot tub clean, clear, and safe.

Let’s dive in… 

What is a hot tub sanitizer?

Hot tub sanitizer is a chemical that kills bacteria and purifies the water. As a general rule, it will be bromine or chlorine-based, but alternative sanitizers do exist. 

Hot tub sanitizer is the most vital component needed in keeping a hot tub healthy.

As a hot tub gets used, it is gradually filled with contaminants and microorganisms that are gross and can lead to diseases.

This is definitely not the kind of water you’d like to soak in, right?

So, there’s a need to sanitize the water often to rid it of these harmful elements. Sanitizers keep your water clean, clear, and safe.

To do this effectively, there are two major sanitizers that hot tub owners use. They are chlorine and bromine.

Let’s check each one out.


Chlorine is the same substance that is in bleach. It’s a naturally occurring chemical element that can be found in seawater and on land. 

Its atomic number is 17 and its symbol is CI. It has a strong chemical smell, that’s what we often perceive in swimming pools and hot tubs. Chlorine is used up faster than bromine.

There are two main ways of categorizing chlorine (but there are 5 types of chlorine): stabilized or unstabilized.

Stabilized chlorine has cyanuric acid, while un-stabilized chlorine does not have it. Cyanuric acid acts as a sunblock that reduces the effect of the sun on chlorine. 

The sun triggers the chlorine to burn off quicker through UV rays, while the cyanuric acid slows down the sun’s effect.


Like chlorine, bromine is a naturally occurring chemical element. It can be found in the earth’s crust and in seawater. Its symbol is Br, and its atomic number is 35.

Unlike chlorine, it produces less of a chemical smell and is sturdier under the influence of heat. But its smell is harder to wash off. It lasts longer than chlorine as a sanitizer.

It also works as an oxidizer. Bromine is not as popular as chlorine, but it’s more effective and a bit more expensive.

I devoted a recent article of mine to explore the differences between Bromine and Chlorine.

Just click the link to read it on my site.

Can I add shock and chlorine to my hot tub at the same time?

Shock and chlorine should not be applied at the same time. Since shock reactivates the sanitizer, it should be added 5-7 days after the initial sanitizer treatment, roughly once a week. Chlorine sanitizer should be applied 2-3 times per week.

Ultimately, adding both would defeat the purpose because one of the reasons for shocking is to enhance the potency of chlorine. Chlorine must have been applied before, and a test should be conducted before the water is shocked.

We’ve already checked out chlorine, but what is shock?

It’s got nothing to do with electricity. It’s when you add a large dose of oxidizer to the tub’s water. 

Which begs the question: what does it do? It sanitizes and also increases the effectiveness of sanitizers. Seeing as it’s an ample dose, its effect is faster. It’s meant to “shock” the water into a clean state.

The aim is to control bacterial growth and reduce the level of contaminants.

As more and more people use a hot tub, or maybe even the same set of people use it often, the contaminants in the water may overrun the chlorine (or bromine), reducing their efficacy.

In the process, they may even bond with them to form harmful chloramines or bromamines.

A hot tub needs to be shocked once a week to reactivate the sanitizers so that they can be freed to do what they’re supposed to do.

But, the process of shocking and sanitizing are two different processes that should be done separately.

Shock, also known as an oxidizer, should be added about once a week. But you can also add a little in after heavy use, such as a party.

In a recent article of mine, I shared more info about what oxidizers do, how they work, and whether I prefer a chlorine shock or non-chlorine shock.

Just click the link to read it on my site. 

How much chlorine do I need to shock my hot tub?

As a general rule, 2 oz of chlorine shock is the correct amount for the average hot tub that holds 5-7 people. But for other sizes, add about 1.25 oz (35g) of chlorine shock per 400 gallons (1500 liters). 

The hot tub cover must be removed, and the pH of the water ought to be checked before the shock is applied.

The cover should be left open for 20 minutes afterward.

Make sure you carefully follow all safety procedures when handling the chemicals.

After you’ve applied the shock, you’d need to wait for 24 hours (to be on the safe side) or 2 hours after applying the shock.

The best thing that should be done each time before you use the tub is to ensure that you test the chlorine levels to ensure they are safe.

Is shock stronger than chlorine sanitizer?

Even though they are often composed of similar chemicals, chlorine shock is stronger than chlorine sanitizer. The purpose of shock is to improve the effectiveness of the sanitizer. So, to achieve this, the shock needs to be more potent. 

Chlorine sanitizers are effective at maintaining the water’s clarity, quality, and safety. But over time, the contaminants in the water negatively affect how well they function. 

The chlorine combines with the contaminants to form chloramines or bromamines, leaving the water smelly, cloudy, and unsafe.

To reactivate the chlorine or bromine, a stronger and ample dose of chlorine (or non-chlorine-based) shock is applied to the water.

It sets the sanitizers free so that they can do their work. Shocks are stronger than sanitizers. 

There are different types of shocks. So, it’s difficult to give an exact figure. But, ballpark, I’d say shock is 2-3 times stronger than chlorine.  

How soon after applying a sanitizer can you use your tub?

Get the lowdown in a recent article of mine. I get into whether there is a difference if you use bromine or chlorine. But I also touch on the differences in wait times for liquid vs. powder. And what about tablets in floaters?

Just click the link to read it on my site.

Should I use chlorine or non-chlorine shock?

A chlorine-based shock always produces clearer, cleaner water. But non-chlorine-based shocks are milder on the bathers and the hot tub. However, if skin irritation is not an issue, always choose a chlorine-based shock.

First off, just in case you’re using bromine and wondering if you could use chlorine-based shocks. Yes, you could. But, do not mix the chemicals or apply them at the same time.

In a recent article of mine, I went into details on why it’s okay to use chlorine-based shocks for bromine tubs, despite the fact that it’s not okay to switch from bromine sanitizer to chlorine without first draining the water.

Just click the link to read it on my site.

Now, let’s go a bit into both types of shocks and which one is better. You can use both.


Obviously, chlorine-based shocks contain chlorine. It can also be known as dichlor. If you apply it to the water, the chlorine levels naturally increase.

I like to add chlorine shock once a week. But I also like to add a little (maybe 1 ounce) anytime there has been some extra heavy use (like when my teen daughters have 5 friends over and they all get in).

But when adding it outside of the normal weekly schedule, always test the water before adding it. Then, test again before the next time someone wants to get in.

Also, make sure to not overdo it.

It’s effective as a sanitizer and oxidizer. But, too much may bleach the cover and pillows. To reduce the likelihood, run your regular jet cycle to aerate the water and leave the cover off for about 20 minutes after adding it.

Non-Chlorine based

Non-chlorine-based shock helps remove contaminants and clear cloudy water, but it doesn’t disinfect. It’s also known as MPS.

It helps in making your chlorine work better by turning combined chlorine into free chlorine. Combined chlorine is chlorine whose potency has been affected by the contaminants. 

So, even if your shock is non-chlorine-based or you’re using bromine, a non-chlorine-based shock would work well with both. 

It’s mild, so you can use the tub after applying it, but to be on the safe side, you might want to wait for at least 20 minutes.


Let’s face it, maintaining a hot tub can be a tad confusing at first. But, in time, you’d see that it’s easy to get the hang of. 

In this article, we went over some vital stuff such as what is a hot tub sanitizer, can it be used at the same time as a shock, and how much chlorine do you need to apply to your tub. 

And, we looked at whether shock is stronger than chlorine, and we wrapped up by looking at chlorine and non-chlorine-based shocks.

Jeff Campbell

Jeff Campbell is a husband, father, martial artist, budget-master, Disney-addict, musician, hot tub lover, and recovering foodie having spent over 2 decades as a leader for Whole Foods Market.

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