How Much Chlorine to Add to a Hot Tub for the First Time?

Buying a hot tub is an investment, and it’s important to take care of it well. Chlorine is something you will need to add frequently but adding too much chlorine can make your skin itch and give you a rash. The first time you fill up your new hot tub with water, how much chlorine should you add?

As a general rule the first time you fill a new hot tub, add 1.5 times the amount of chlorine that is recommended for weekly chlorination for the size of the hot tub. The goal is 5 to 8 parts per million, as opposed to the daily goal of 2 to 4 ppm. This first-time boost helps to rid the hot tub of any bacteria from initial setup, transport, or storage. 

Getting chlorine levels right on the first setup of the season is important, especially if you have a new hot tub or it has been in storage for a while. In this post, we’ll discuss how to get your hot tub set up for the first time, including the levels of chlorine and other chemicals, as well as how to take care of it to keep it at its best all season long.

How Much Chlorine to Add to a New Hot Tub for the First Time
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Why does a new hot tub need more chlorine?

New hot tubs need a higher-than-usual amount of chlorine when they are first set up because the water has not been circulated through them yet. Chlorine reacts with organics in the pipes to create compounds called trihalomethanes, which can make you sick if too many build up in your system. 

Trihalomethanes also react with the chemicals in your hot tub to create a process called chlorophenol formation. The result of this is that you might have off-gassing or chlorine odors from your newly set up hot tub.

Hot tub starter kits

When adding chemicals to hot tub the first time, these convenient packs of chemicals and accessories get you started with your hot tub when you purchase it. The Hot Tub Things Starter Kit comes complete with all the chemicals you will need and a “Frog” which is a chemical dispenser that flips over when it needs refilling.

How often to add chlorine to a hot tub?

A common amount of chlorine to add to a hot tub is about one teaspoon of granules per 100 gallons. Of course, this depends on what type of chlorine granules, tablet, or liquid you are using. 

Refer to your manufacturer’s directions for what type of chlorine is best for your spa. In general, however, for the first fill of a hot tub, you want the chlorine level at 5 to 8 ppm, whereas it can ride between 2 to 4 any other day. 

The amount of chlorine needed depends on the size and shape of your hot tub, as well as how many gallons it holds. If you’re not sure what’s perfect for your tub, start with one ounce per every 250 gallons. If that’s not strong enough, you can add more chlorine to the water when it looks like there may be bacteria growing in your tub and start with one ounce per 100 gallons of hot tub water.

How to add chlorine to a hot tub

The first step is to test your hot tub water. Test the chlorine level of the water with a kit that you can buy at your local pool or spa supply store.

Many municipalities already chlorinate the water, so you’ll want to know your baseline before you start adding chlorine. 

From there, it’s simple. Add the recommended amount for your size tub, in whatever form you are using. 

Pro-tip: If it’s a new hot tub, test your water before you fill your tub. Take a sample to your hot tub dealer and let them test it to see what chemicals will best fit the needs of the water from your tap! 

Why add chlorine to hot tub water? 

Chlorine is the most common chemical used in a hot tub, and it’s added for disinfectant purposes. 

It helps kill bacteria, viruses, fungi, algae, and other microorganisms that may make you sick if they get into the water. Without chlorine or another sanitizer, the hot tub water will get cloudy, bloom algae, and potentially mold. 

While there are other sanitizers that can be used, chlorine is a popular choice because it is cost-effective, easy to use, and great at what it does. 

How to Add Chlorine to a Hot Tub

What does it mean to shock hot tub water? 

A shock is adding a higher dose of a chemical, usually one that contains chlorine or non-chlorine sanitizer, to kill anything in the water. It can also be called oxidizing. It removes organic contaminants and removes what’s leftover (chloramines) when chlorine kills bacteria. 

If the filter becomes clogged and can’t keep up with excess dirt, bacteria start to build up in your tub’s plumbing lines. A shock will turn all of those bad things into harmless chemicals you can just dump down your drain when you’re done.

Different chemicals can be used for different types of shocks: bleach is typically used for a chlorine shock, while non-chlorine shocks usually use bromine. 

How to shock your hot tub

It’s a pretty simple operation to shock your hot tub. Just be careful in handling the chemicals, as always, by wearing goggles gloves and covering your skin. 

  • Take off the hot tub cover
  • Test the water
  • Get it to a pH of about 7.5 for best results when using the shock
  • Keep the pump on and turn off the jet
  • Measure the shock and carefully add it according to directions

Now you can let the hot tub rest uncovered for about 30 minutes. Test the water before using the tub and if you are not going to use the tub soon, cover it up to keep that newly shocked water nice and clean.

How often should you shock your hot tub?

It is recommended that you shock your hot tub weekly, maybe more, depending on how much use it gets. The important thing is to always test the water before and after – and to protect yourself while using strong chemicals. 

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 Much Chlorine to Add to a Hot Tub for the First Time? 1

What if you add too much chlorine to hot tub water?

Adding too much chlorine to a hot tub can cause burning, irritation, and even vomiting. If you’re using bleach as your chemical of choice for shocking the water, it’s best to do so in the morning before people use the tub later that day. This way, there isn’t any residual chlorine lingering around when someone gets into the water.

How to tell there is too much chlorine in your hot tub

Most people think the “bleach smell” means that there is too much chlorine in the hot tub water. In fact, the opposite is true. The characteristic smell of bleach results from what chlorine does: it is the resultant chloramines left behind, as the chlorine breaks down in the water.

So, when you smell that bleachy smell, it actually means your chlorine has done its job and has run out. 

Always test the water to know for sure and either dilute it with fresh water or let it sit for a while and test again. You can also add a chlorine neutralizer to reach a safe level of chlorination again. 

Should you shock a hot tub before end-of-season storage?

No, you don’t need to shock it again since it’s not going to be used for a while. 

It’s best to drain, thoroughly clean, and sanitize your hot tub before storage and winterize it according to the directions in the manufacturer’s manual. 

You may want to consider keeping your hot tub open all year, even if it gets very cold in the winter where you live. There is nothing more enjoyable than sitting in a lovely hot tub on a cold day, with snow all around, feeling warm and relaxed. Your neighbors may think you are mad but that will just be envy.


If you’re going to be using your hot tub for the first time, it is important that you clean and disinfect it with a strong dose of chlorine. The chemicals in this solution will remove all bacteria and contaminants from the water as well as help circulate them through the spa to ensure complete coverage.

In addition, a regular shock of the hot tub water will ensure your hot tub is continually free of bacteria, contaminants, and chloramines. With this regular chlorine maintenance, your hot tub soaks will be not only relaxing but also sanitary all season long.