How to Shock a Hot Tub – A Complete Guide

  • By: John Parker
  • Last Updated: November 20, 2022

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 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!

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

Shocking your hot tub is not a difficult process. It is necessary to shock the water in your spa using a spa shock treatment 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. 

shocking a hot tub
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Table of Contents

What does spa shock do?

When you shock your hot tub, you are cleaning the water by killing bacteria and other contaminants. This will ensure that you, your family and your 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 shock chemicals that will get the job done for the type of sanitizer you use. By that, I mean chlorine vs bromine.

What is the best shock for my hot tub?

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 shock (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. Using this type of shock means you can use the tub again much sooner than using chlorine shock.

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.

I recommend using SpaGuard Spa Shock or SpaGuard Spa Shock-Oxidizer

SpaGuard Enhanced Spa Shock 6#

SpaGuard Spa Shock-Oxidizer, 7lb

Hot tub shock – step-by-step guide

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

how do you shock a hot tub

1. Open the cover and turn on the pump

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

2. 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.

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. You will normally need to know how many gallons your hot tub holds to work out how much shock treatment to use.

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.

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.

5. Pour the mixture in the spa water

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

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 my article How Long to Wait After Shocking.

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!

what does shocking a hot tub do - hot tub party

Can you over shock a hot tub?

If you make a mistake with the amount of shock to add to the hot tub, perhaps a mistake in measuring or in calculating how much shock, then it is possible to over shock.

This means that the free chlorine levels will be very high. Far too high to even consider using the hot tub.

The ways to deal with this are:ç

  1. Drain the hot tub and refill.
  2. Partially drain the hot tub and refill. Retest the chlorine level.
  3. Leave the hot tub cover off and run the pump as much as possible to help dissipate the chlorine. Retest the chlorine levels occasionally and don’t use it until they have dropped to normal levels.

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How to Shock a Hot Tub - A Complete Guide 1

Frequently asked questions about shocking hot tub water

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.

How much shock for 250 gallon 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 pool shock (calcium hypochlorite).

How much shock for 250 gallon hot tub?

The amount of shock treatment 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.

Do you run jets when shocking hot tub?

You should run the jets but without the air when you add shock to the hot tub so that it is properly mixed throughout the water and the plumbing.

Can you shock a hot tub with chlorine tablets?

Chlorine tablets will invariably also contain cyanuric acid (CYA) which is a stan¡bilizer used to stop chlorine from being used up too quickly. It is not suitable as a hot tub shock.

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 need to 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.

Read also: Add chlorine to a new hot tub

Some last thoughts

Knowing how to shock a hot tub is 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, why you shock and what shock is best to use.

You should also learn when to shock.

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

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