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How to Shock a Hot Tub

By Matt Giovanisci | Updated: September 19, 2019

We have some shocking news for you. Sanitizer isn’t enough to keep your hot tub sanitary for the long term. Shocked? Well, it only makes sense. It wears off after a while, and sometimes it’s just overrun by more contaminants than are usually in your hot tub.

But the most unshocking reason to use spa shock? It’s just smart. That water remains in your hot tub for weeks or months at a time. Don’t you want to make sure it’s always completely clean and sanitary? Of course you do. Which is why you must learn how to shock your hot tub.

What is Spa Shock?

First, let’s be clear—this has nothing to do with electricity. That definitely doesn’t mix with water.

Hot tub shock is a large dose of oxidizer used to “shock” the water into a clean state after it’s been contaminated somehow. It performs three main functions.

It Removes Organic Contaminants

Every time you get into your hot tub, you take all kinds of organic contaminants in with you. Shampoo, lotion, makeup, sunscreen, hair, dead skin cells, and remnants of whatever else your body has come into contact with that day.

And if more than one person is using your hot tub on a regular basis? Multiply all those contaminants by the number of people soaking in the water and … that’s math you don’t really want to do.

You can reduce the amount of organic contaminants by showering—or at least rinsing off—before every soak. But that’ll only go so far. The remaining yucky stuff will be attacked by your sanitizer. But that also only goes so far.

After a while, your sanitizer gives out, and those contaminants build up in the water and create problems like hot tub scum or cloudy hot tub water. Blech.

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It Kills Bacteria

There’s regular bacteria that’s just gross and sometimes causes discoloration on things like your shower curtain. That pinkish stuff? It’s not rust. It’s bacteria. Wash your shower curtain with bleach to get rid of it.

And then there’s the really nasty bacteria that causes illness. Hot tubs are known for being incubators for three specific types of illness-causing bacteria:

These and all other bacteria can be kept at bay by keeping your hot tub water balanced and ensuring that sanitizer levels in particular remain steady. But in between water tests and chemical additions, sanitizer is used up to keep the water clean.

Spa shock will give it a boost and kill anything that might’ve been cropping up in the water before it has a chance to make anyone sick.

It Removes Chloramines or Bromamines

You know that “chlorine smell” you associate with public pools and hotel hot tubs? It’s not the chlorine that smells; it’s the chloramines.

As chlorine is used up killing bacteria and removing organic contaminants, it produces waste products. Those are chloramines, they’re what you smell. They’re also what you’re breathing in until you get the sanitizer level back where it needs to be.

Hot tub shock brings that level up quickly, and eradicates chloramines from the water, getting rid of the smell, and allowing you to breathe easier.

If you use bromine as your sanitizer, it also produces waste products called bromamines. They’re not as noxious as chloramines, and you may not even notice them. But they’re still not something you want to breathe in. Keep the bromine level steady, and shock regularly.

So you see why shocking your hot tub is an essential part of caring for it. But not all shocks are created equal. Some types eradicate all contaminants, while others only work on a few.

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Hot Tub Shock Types

You’ll find four main types of spa shock available. But only two of them are viable for hot tubs.

Calcium Hypochlorite

Also known as cal hypo, it’s inexpensive and convenient because it’s widely available. But you should not use it to shock your hot tub. It’s better for pools.

Cal hypo is unstabilized chlorine, which means it’ll lose about 95% of its effectiveness after just a few hours of heat exposure in your hot tub. It also contains calcium, and in a small body of water like the one in your spa, it will quickly deposit scale on surfaces and components, potentially damaging them.

Important: Only use chemicals labeled specifically for use in hot tubs. It’s a smaller body of water, and it’s heated to much higher temperatures than pools, which means chemicals that work fine in pools will react differently in spas. Prevent damage—and voiding your manufacturer’s warranty—by only using spa chemicals.


Technically named sodium dichloro-s-triazinetrione or dichloroisocyanuric acid, it’s a lot easier to call it dichlor shock. It’s the active ingredient in most brands of hot tub shock.

You can usually add it directly to the water without dissolving it first, but always follow the manufacturer’s instructions on the package.

As you can tell from that second scientific name, it contains a small amount of cyanuric acid, which means it’s stabilized, which means it will stand up to the spa’s heat. Still, keep a close eye on your sanitizer level, and if your hot tub is outside and not under any structure like a gazebo, shock it at dusk or night to keep the sun’s rays from eating the chlorine away too quickly.

Lithium Hypochlorite

You may see this type of shock at your local hot tub or pool supply store. But we doubt it. Lithium hypochlorite isn’t as widely available as it used to be because most lithium is now used to make lithium batteries. This also means the cost of the raw material has gone up a lot, making the shock (if you find it) more expensive than it used to be, too.

Do yourself a favor, and stick with dichlor shock. It’s less expensive, and you can find it anywhere.

Non-Chlorine Shock

The most important thing to know about non-chlorine spa shock is that it is not a disinfectant. This means it does not kill bacteria. So why even use it?

Well, its most common active ingredient, potassium peroxymonosulfate, is an effective oxidizer. Used weekly, it does a great job of getting rid of organic contaminants (skin cells, lotions, etc.), and clearing the water if it’s become a little cloudy due to those contaminants.

Also, if you use chlorine as a sanitizer, it activates free chlorine, the type of chlorine needed to kill bacteria. It does the same thing for bromine.

Which Spa Shock Should I Use?

Well, that depends on which sanitizer you use.


Use chlorine shock. This one’s a no-brainer, right?. But you can also use non-chlorine shock more frequently to address organic contaminants and keep the water clear between regular chlorine shocks.

If you do that, test often and keep an eye on the chlorine level to make sure it doesn’t drop below 1 ppm. You actually want to keep that at 3 ppm, the higher end of the recommended range.

But if you use your hot tub often, or you have a high bather load (several people use it), we highly recommend sticking with chlorine spa shock to kill bacteria and keep the water sanitary.

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Use chlorine shock. But, just as with chlorine, you can also use non-chlorine shock for all the same reasons.

Again, we recommend sticking with chlorine shock if you have a high bather load.

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Use biguanide shock. It’s actually hydrogen peroxide, but not the kind you keep in your medicine cabinet, so don’t think you can just pour in a bottle of that cheap stuff from the drugstore and be good to go.

Manufacturers that make biguanide sanitizer usually have a whole line of products (oxidizer, water clarifier, test strips) made to work with biguanide.


Use non-chlorine shock. If you’re using a spa mineral sanitizer, you already know you have to supplement with a little chlorine to get the full sanitizing effect. But that chlorine level should only be 0.5 ppm, so if you used chlorine shock, you’d likely end up with too much chlorine in the water.

This isn’t to say you can’t ever use chlorine shock. If you’re having a problem with bacteria, algae, or the chlorine level is at zero, chlorine spa shock is the way to go.

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Salt Water

Use chlorine shock. The salt chlorine generator is turning salt into chlorine, which is what’s sanitizing your spa. This makes chlorine shock the best choice.

You can also use non-chlorine shock if you’re concerned about the chlorine level being too high.

Ultraviolet, Ionizer, or Ozonator

Use chlorine shock. Dichlor is compatible with these systems, but always follow the manufacturer’s instructions.

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01/25/2023 02:10 pm GMT

The Best Way to Shock Your Hot Tub

If you’ve never learned how to shock a hot tub, it’s not a complicated process. But you do need to take a few precautions and follow the steps in a certain order to get the most benefit from spa shock.

You’ll need:

Once you have your supplies gathered, you can get to work.

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Uncover Your Hot Tub

And leave it uncovered throughout this process. Once you add the shock, some of it needs to off-gas—dissipate—from the water.

This also applies to the floating thermal blanket (if you have one), and any accessories that may be floating in the water.

Important: Do we really need to say that no one should be in the hot tub when you add spa shock to it? Or when you add any chemicals to it? We’re gonna say it anyway, for the people in the back.

Test the Water

Before shocking your spa, the pH must be at the correct level, between 7.4 and 7.6. High or low pH in your hot tub will affect the shock’s ability to work as well as it should.

If it’s not in the right range already, adjust it, then continue with shocking.

Turn Off the Blower

The circulation pump needs to remain on to distribute the shock through the hot tub. But turn off the jets so the water is moving but not too agitated, and to prevent the spa shock from off-gassing too quickly.

Put On Your Safety Gear

Shock (and every other chemical you put in your hot tub) is, well, a chemical. You don’t really want it on your skin, and you definitely don’t want it in your eyes.

In addition to gloves and safety goggles, consider wearing long pants, a long-sleeved shirt, and closed-toe shoes.

If your hot tub is inside, open a window, turn on an exhaust fan, or both. However you do it, make sure there’s good ventilation in the room before you open and use any chemicals.

If your hot tub is outside, try to shock it when it’s not windy. If there’s a breeze, stand upwind from the hot tub, and keep your hands as close to the water’s surface as possible to prevent chemicals from blowing anywhere but into the hot tub.

Important: If you spill any shock, clean it up immediately and dispose of it safely. Always keep spa shock (and all other chemicals) out of the reach of children and pets at all times.

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01/25/2023 09:34 am GMT

Measure the Shock

You’ll never just pour shock into the spa directly from its container. Eyeballing it is not an option. Measure the amount of shock you need for the amount of water your hot tub holds. Check the shock’s label to find this information.

And if you’re not sure how many gallons of water are in your hot tub, consult the manufacturer.

Shock It!

Carefully add the shock to your hot tub using the method prescribed by the shock’s manufacturer.

Leave the Hot Tub Uncovered

Don’t cover the spa for at least 20 minutes to allow the spa shock to disperse and dissipate.

If you’re not going to use the hot tub immediately after shocking, do put the cover on after 20 minutes to prevent evaporation.

A Few Shocking Questions

Now that you know how to shock a hot tub, you probably still have a few questions. Well, we’ve got answers.

How Long Before I Can Use the Hot Tub Again?

There’s no hard and fast rule about when you can get into your hot tub after you’ve shocked it. It’s going to depend on when the sanitizer level has dropped back down to where it’s supposed to be.

The only way you’re going to know that’s happened is by testing the water. But also check the shock manufacturer’s instructions for any special considerations.

How Often Should I Shock My Hot Tub?

Easy question with a simple answer: weekly. Actually, the answer is at least weekly. If your hot tub gets a lot of use, or you have a lot of people in it at once—or both—you may want to up that to twice a week.

Just remember to always test the water before you shock to make sure the pH is where it needs to be, and before you get back into the spa to make sure the sanitizer is where it needs to be.

When Should I Shock My Hot Tub?

If it’s indoors, anytime is fine. If it’s outside, and it’s not underneath a structure like a patio cover, wait until dusk or night.

Even if you’re using dichlor, which does contain some stabilizer, it’s best to prevent the sun’s rays from burning off the chlorine before it has a chance to work.

Shocked by How Easy That Was?

Now you know how to shock a spa! Which also means now you have no excuse to skip it. But trust us, even if maintaining your hot tub is a royal pain sometimes, you’ll be glad you did when you can soak in clean, sanitary water with no worries about nasty stuff like algae or bacteria.

Remember, always read the manufacturer’s instructions before you begin. Preventing a chemical mishap is much better than possibly have to drain your hot tub and start over.

Happy Soaking!

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.
A Cheat Sheet For Balanced Hot Tub Water and Crystal Clear Soaking.
Download this FREE printable cheat sheet to keep your hot tub clean and clear. You’ll never worry about your hot tub again with this easy-to-use guide.
Click Here For The FREE Cheat Sheet