How to Shock a Hot Tub – A Complete Guide

Have you ever been about to take a nice relaxing dip inside your hot tub? Then, right before jumping in, you notice you have cloudy water, the hot tub water feels slimy or there is an unpleasant odor. If that is the case then it’s time to get it cleaned, aka you need to shock! Not you, your tub! 

When you shock a hot tub, you are essentially cleaning the water. You introduce a high dose of chlorine shock or non-chlorine shock in the hot tub water. The shock will kill bacteria and remove organic materials and other contaminants such as chloramines. 

Shocking your hot tub is not a difficult process. It is necessary to shock the water in your hot tub if you want to keep it clean. The water will not just clear up, but this process has many more benefits that you can read about below. 

How to Shock a Hot Tub
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What does it mean to shock a hot tub and how is it done?

When you shock your hot tub, you are cleaning the water by removing bacteria and other contaminants. This will ensure that you, your family and guests can take a clean and relaxing soak in healthy water conditions.

Before diving deeper into how you can shock your hot tub, it is first essential to understand the different hot tub shock chemicals that will get the job done for the type of sanitizer you use.

What is the best shock for my hot tub?

The type of spa shock you use to eliminate organic contaminants largely depends on the type of sanitizer you use in your spa. There are basically two types of sanitizer that are used in hot tubs which are chlorine or bromine.

You can also have salt water hot tubs but these are effectively the same as chlorine hot tubs as the salt (sodium chloride) is converted to chlorine which then acts as the sanitzer.


Chlorine is the most popular sanitizer used in hot tubs. One of the biggest considerations of hot tub owners when it comes to choosing between chlorine or bromine is cost. Chlorine is normally cheaper. Chlorine can be less effective once the water temperature rises above 28 degrees.


Bromine is also used as a sanitizer. The benefits of bromine are that it doesn’t lose its effectiveness when the water temperatures are higher and also because bromine does not have a strong smell which chlorine can often have. Bromine does come at a higher price.

Which type of shock to use?

The most usual type of shock to use with a chlorine hot tub is, unsurprisingly, chlorine. There are two main types of chlorine shock which are dichlor (dichloroisocyanuric acid) and cal hypo (calcium hypochlorite). Most brands of spa shock contain dichlor and that would be the type I would recommend. Cal hypo is more suitable for shocking swimming pools. You can also use a non-chlorine shock which is known as an oxidizer.

SpaGuard Enhanced Spa Shock 6#

In a bromine hot tub you can use either chlorine based or a non-chlorine. Personally I would use a non-chlorine oxidizer once a week.

SpaGuard Spa Shock-Oxidizer, 7lb

How to shock a hot tub

Now that you have picked the product you want to use, it is time to tell you how shocking the hot tub gets done. If you’re going to clean out the water in your tub, you can do so following these steps:

Testing the water in a hot tub

1. Check the water condition and pH levels. 

You can use either a test strip or test liquid to check the levels of the water in your hot tub.

One of the readings these will give will be the pH (ie whether it is acidic or alkaline). The pH level should be between 7.2 and 7.6. If it is above or below this range you should adjust it before you shocking.

2. Open the lid and turn on the pump

The circulation will make the water move around. When the water is moving, the shock will respond quicker. 

3. Mix your shock product 

Carefully read the labels that explain how you should mix the shock. Most shocks in the form of chlorine granules need to be pre-mixed.

Some spa shocks come in small sachets which you can just sprinkle over the water without premixing. If that is the case then skip this step.

As with all pool and hot tub chemicals, make absolutely sure to keep them outside the reach of children.

4. Place the mixture in the spa water 

Poor the spa shock mix around the hot tub. Always do this carefully.

5. Turn on the spa circulation pump

You need to ensure that the shock is evenly distributed throughout the hot tub, including the pipes and plumbing so running the circulation pump will make sure this happens. Do not turn on the air (bubbles) though.

You should also leave the cover off during this process as this will allow and gases that are produced to dissipate. It will also most likely keep the pump running to keep up the temperature. If your spa is inside then make sure the area is well ventilated.

6. Wait for the shock to do its job

This process can take anywhere between 20 minutes and 24 hours depending on the type and amount used. See the section How Long do I Have to Wait After Shocking hot tub Before Using it Again? below.

7. Test the water levels to see if it is safe to get in

Retest the water using a test strip or liquid test and don’t use your hot tub until the chlorine level is back to safe levels.

It is that easy, anyone can do it!

How often should I shock my hot tub?

The opinions on when you should shock your hot tub are divided. Some say every week. Others recommend doing it at least once every two weeks. One thing is clear, you should do it on a regular basis.

It really depends on how often you use the spa, where it is situated, the water temperature, etc. In the end, it is important that you are bathing in clean water that does not make you sick. When the hot tub is used often, then using spa shock once a week is highly recommended.

Did you have lots of guests over so the spa has a high bather load? Then shocking it right after that occasion would be advisable so that the next time you go to your hot tub, you won’t find the water dirty and cloudy.

It is essential to be smart about it. If you can see the water changing color and going cloudy, then doing an extra shock is a good idea and certainly won’t hurt.

There is a difference between a hot tub that has been shocked with chlorine or non-chlorine based shock. Chlorine shock can be hard on your hot tub’s plumbing. Therefore using this chemical weekly is not advised.

Hot tub party - How often should I shock my hot tub

What are the benefits of shocking my hot tub?

Some people wonder why they should shock their hot tub when they use plenty of sanitizer. Unfortunately, only using sanitizing products won’t eliminate some of the things in the water that spa shock will. Therefore, shocking your hot tub has many benefits.

1. It will eliminate organic contaminants

Everyone that jumps inside your hot tub takes some sort of organic material with them. Think of contaminants like shampoo, sunscreen, perfumes, oils, etc. The sanitizer will then react with them and produce chloramines.

2. Keeps water clean and not cloudy

The water will get cleared of bacteria and organic matter, keeping the water fresh and clear. When the water is not clear, this is a good indication that the hot tub needs to be shocked.

3. Removes unwanted bacteria in the water

As you might imagine, when water sits at a high temperature in one area for a long time, bacteria might develop there. So to kill bacteria that can potentially make us sick it is necessary to use spa shock.

4. Improves your hot tub’s life span

When your hot tub is contaminated, this will eventually wear out the hot tub. Especially the places that water gets into, such as the pump and filters for example.

When should I shock my hot tub?

If you want to shock your hot tub, you should do this before getting in or after. The shock chemicals you put in the water are highly dosed to eliminate all the things you don’t want inside your water. The shock chemicals are not safe to bathe in while at a high concentration. They can be very harsh on the skin and bad for your lungs. Swallowing the water while the chemical reaction is taking place can make you sick. 

Allow the shock to do its job for at least twenty minutes before thinking about getting in the tub. Always read the labels that are on the chemicals you buy. They will advise you how long it takes for the reaction to be complete and when it is safe to get back in. The average duration is somewhere between 20 minutes and as much as 24 hours. This will depend on the product, how dirty the water is, and the dosage. 

If you want to be sure that you can bathe in your hot tub again without it being unsafe, you can use tools to test the water levels. You can buy test kits or test strips.

Hot Tub Maintenance Course

I bought this course some months after I bought my first hot tub and was struggling with maintaining it. It was money very well spent and it has paid for itself many times over the years.

How to Shock a Hot Tub - A Complete Guide 1

Should you shock before or after using the spa?

When people ask if they should shock before or after using the spa my answer is: both! If you are planning to get in soon, it is best to do it after spending some time inside the water. On the other hand, if you plan to bathe in a few hours, then shocking it before should not be a problem. 

That being said, it is advised to shock the spa after you have used it. This will give the chemical reaction all the time it needs to clean the water and for it to get down to normal levels. The normal levels will keep your skin much happier.

How long do I have to wait after shocking hot tub?

As mentioned above, the time that you should wait after shocking the hot tub differs. This has to do with a few factors.

1. The type of shock product

Generally, you will have to wait longer before it is safe to use when using chlorine shock than non-chlorine shock. In most cases, when using a non-chlorine shock (which is an oxidizer) you can get back in quite quickly, so it is ideal if you test your water before a spa party and realize you need to shock but have little time before the party.

Always look at the labels of the shock product you have bought. If you are not sure, then either look the product up online or ask a professional.

2. How dirty the hot tub is

As you can probably imagine, the more you use the hot tub, the dirtier it will get. Also, not cleaning it or shocking the hot tub for a while will leave more bacteria and other contaminants inside the water. Often you can see this by the color of the water. The dirtier and more cloudy it is, the more time it will take for it to get thoroughly cleansed. You will most likely also have to put a higher dosage of shock in the water. 

3. The concentration

The higher the concentration of the shock product, the longer it often takes for the water to stabilize to normal levels again. The normal levels are necessary for your bathing to be safe and healthy.

4. How often you shock the hot tub

The more frequent you shock the hot tub, the cleaner the water will be. Therefore, using a lot of spa shock in a high concentration is most likely not necessary. If you use less spa shock and at a lower concentration, it will take less time for the water to reach its normal bathing levels. 

When should I shock my hot tub?

Frequently asked questions about hot tub shock

Before rounding up this article, I quickly want to answer three more questions that I get frequently. The answers to these questions are helpful to understand when you are planning to shock your hot tub.

Can I use pool shock in my hot tub?

If you only have a hot tub and not a swimming pool too then this probably isn’t something you need to worry about.

It can sometimes be confusing to know if pool chemicals can also be used in hot tubs. Some products say it is made for hot tubs, some say it’s for pools, and some say both.

You can use pool shock in your hot tub but you must be careful that you use an amount appropriate to the smaller volume of water in the hot tub. Generally it is recommended that you only use dichlor (dichloroisocyanuric acid) and not cal hypo (calcium hypochlorite).

How much shock do I need for a 250 gallon hot tub?

The amount of shock that you put inside a 250-gallon hot tub differs per product. If using chlorine-based shock then you should approximately 1/16 cup of spa shock. Keep in mind that it is easier to add more later on than to take out. If you feel like the hot tub water is not getting clean after about 30 minutes, you can always add a bit more.

Testing the levels in your hot tub will help you figure out the amount that works in your hot tub.

Should you shock a hot tub after filling?

When you refill your hot tub, you are adding clear and clean water to the tub. After refilling, you will most likely add some form of sanitizer and cleanser. Therefore, it is not always necessary to shock the hot tub right after filling it (you don’t sanitize your bath water after all).

However, if many bathers use the hot tub, then shocking becomes necessary. Also, when a week has passed after the refill, it is time to use hot tub shock in order to raise the free chlorine levels.

Some last thoughts

Shocking your hot tub is a process that is very important to keep your hot tub clean and safe to use. How you shock the spa will determine how clean, clear and uninfected your bathing water will be. After reading this article, we hope you now understand how to shock a spa, what products are best to use, and how often the shock process should take place.

After all, we all want to be able to get into our spa without having to clean it first!

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