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How Long Does it Take for Chlorine to Dissipate in a Hot Tub?

By: Author Jeff Campbell

Posted on  - Last updated:

Categories Hot Tub Operational Tips, Hot Tub Water Chemistry

Many times I’ve wanted to get in my hot tub, checked the water and realized I needed to add chlorine, and then had to wait. So how long does it take for chlorine to dissipate in a hot tub?

After adding liquid or powdered chlorine sanitizer, wait at least 30 minutes for it to dissipate in the water to make it safe to soak in. After adding chlorine shock, which is more potent, it can take up to 2-4 hours to dissipate. Running all the jets with the cover off will speed up the process.

But of course, always check the water before getting in.

After all, you may have added too much chlorine or too little. And either way, depending on how off the levels are, it might not be safe to soak in.

But what about tablet floaters? Or bromine? Don’t worry. In this article, we’ll get into all that and more.

Let’s jump right in.

hot tub on deck with mosquito net

How soon can you go in a hot tub after adding chlorine?

As a general rule, after adding your regular chlorine sanitizer dose, you should wait 20-30 minutes before getting in. Then, leave the pumps running and the lid off to allow the gasses to dissipate into the air.

It is often the chlorine gas or chlorinated water vapor that causes the most irritation to the eyes.

The time varies, but this recent article explained how long to wait after adding sanitizer to your hot tub. Just click on the link to read it here on my website.

Be guided by your test strips.

The level of chlorine should be between 1 and 3 parts per million (ppm). If it is above this, it can cause irritable skin and eyes. Above 5 ppm can result in nausea, headaches, and breathing difficulties.

If you’re using bromine as a sanitizer, you can probably enter a bit sooner – say after 10-20 minutes, but again, test the water beforehand.

Shocking your hot tub is the process of giving a high dosage of chlorine to reactivate the sanitizer by increasing the available free chlorine in the water.

After using chlorine, you should allow 24 hours for the level to drop, but if you use non-chlorine shock (e.g., potassium monopersulfate), you should be able to get in after 10 minutes.

Always test the levels after shocking the water before getting in. These times are dependent on a number of factors, such as the volume of water and the temperature outside. 

Does chlorine evaporate from a hot tub?

It is not the chlorine that evaporates from a hot tub but the water containing the dissolved chlorine. Although the temperatures in a hot tub are not sufficient to turn the water into steam, water vapor can appear at much lower temperatures.

Now if you mean does heat from the hot tub water use up the chlorine quickly, that answer is yes. Chlorine is not very well resistant to both heat and sun. That’s why it has to be added so often to swimming pools (and why public pools tend to be heavy-handed with it).

And that is why many hot tub owners like bromine better for sanitizer; it holds up better in the heat.

But this is how evaporation in a hot tub works.

The movement of the water’s surface allows some molecules to escape into the air. The rate at which this happens depends on a number of factors:

  • The temperature of the air and water
  • The humidity of the air
  • The size of the surface exposed

A hot tub has a large surface area, and the air above it is very humid, so the molecules of water are almost immediately condensing into micro-droplets in the air.

This effect is increased when you turn on the jets. 

The water is agitated and becomes aerated, and this increases the rate of evaporation. Also, the rapid movement of the water causes the chlorine to dissolve quicker, and so you lose more when the jets are on.

This is all part of a natural process and another reason you should constantly check the sanitizer level in the water.

Even at cooler temperatures and with the pump in economy mode, the heat from the sun can cause evaporation. To combat this, you need to keep the lid in place when the hot tub is not in use.

If you’re still confused about the difference between chlorine and bromine, check out this recent article. I get into the exact differences between the two. But I also explain why I prefer one over the other.

Just click on the link to see it here on my website.

What do I do if my hot tub has too much chlorine?

If the test strip shows the chlorine levels in your hot tub to be too high, you can wait 1-2 days for the levels to drop naturally, drain off a portion of the tub and top off with fresh water, or use a chlorine neutralizer such as sodium thiosulfate.

CLICK HERE to check out the best chlorine neutralizer on Amazon.

But, if you find there is a smell of chlorine when you lift the lid, it doesn’t necessarily mean you have too much chlorine in there. It is more than likely caused by chloramines. Chloramines develop when the chlorine in the water mixes and reacts with the biofilm, which is caused by things like body lotions, perfume, even dead skin.

But first, check the chlorine level with a test strip – it should be between 1 and 3 ppm, but if it is over 5, then you have too much chlorine in your hot tub. If this is the case, then as I mentioned, you have three options:

  • Leave it a couple of days and let the level drop naturally
  • Use a chlorine neutralizer such as sodium thiosulfate
  • Drain off a few inches of water and top off with fresh water, adjusting the chemicals as needed

Sunlight depletes chlorine, so if you are in no rush to get back in, leave the lid off for a while to speed up the process. Turn on the jets as well – the agitation of the water will release the chlorine into the air as water vapor.

If you use a chlorine neutralizer, add it slowly, checking the chlorine level as you go. Check the pH and alkalinity levels after this and adjust as necessary.

In a recent article, I pointed out the danger of going into a hot tub with a high chlorine level. Chlorine is vital for your safety and the cleanliness of your hot tub. But there are some significant dangers of getting in when levels get too high.

You can read it here on my website by just clicking on the link.

How many chlorine tablets should I put in my hot tub?

4-6 one-inch chlorine tablets added weekly to a floater will be correct for the average hot tub that holds 5-7 people. But always check the levels before entering. During periods of heavy usage, more tablets could be necessary.

You can apply chlorine in different ways – granules, tablets, or even in liquid form – but the best way to get a consistent dosage every time is to use tablets. Most makes also have added algicide and clarifier to help keep the water clear.

Whatever product you use, make sure you use one made for hot tubs and NOT just swimming pools. Pool tablets are much larger, around 3-inch, whereas spa tablets are just 1-inch across.

Chlorine tablets are slow to dissolve, so they discharge the chlorine over a long period of time.

Some people see this as a disadvantage and feel the need to add more tablets because they don’t get that chlorine smell. This is a big mistake and will result in you overdosing your hot tub.

You only need 1 tablet for a 300-gallon tub – how often depends on usage. The average hot tub is most often between 500 and 600 gallons.

Floating dispensers are a great way of making sure you get a slow release of sanitizer, but note, if you use a dispenser for chlorine, make sure and wash it thoroughly before switching. The chemical reaction can be dangerous.

One dispenser I like on Amazon is by Hydro Tools. It has nearly 7,400 reviews on Amazon, and almost all are 5-stars. Click on the link to read the reviews and check the latest price.

It’s easy to use, and the holes in the side can be closed off to reduce the speed at which the sanitizer is released.

Not sure what chlorine tablets to get?

I like these 1” chlorine tablets from Clorox on Amazon. Almost 5,000 near-perfect reviews can’t be wrong!

What about bromine sanitizer?

If you decide to use bromine sanitizer, the ideal tablets for this dispenser are the Leisure Time bromine tablets on Amazon. You can get them on Amazon, where it has nearly 600 ratings, and again, almost all are 5-stars.

Using bromine as a sanitizer doesn’t prevent you from using chlorine to shock your hot tub water. Read about it in this recent article. But you never want to just switch from chlorine sanitizer to bromine sanitizer without first changing the water.

Just click that link to get all the details right here on my website.

How long does chlorine take to sanitize the water in a hot tub?

Chlorine will begin sanitizing the water almost immediately but can take as much as 30 minutes to fully sanitize a hot tub starting from no or low chlorine. Liquid chlorine will impact the water the fastest, whereas tablets take a long time to dissolve fully. Chlorine granules will be in the middle of that range.

And the important thing is to aim for around 3ppm. If the full power of the chlorine was released at once, it would rocket way above that, and you would not be able to use your hot tub.

Chlorine will kill bacteria and viruses at different rates, depending on the strain. 

E.coli will be destroyed in less than a minute, but for Hepatitis A, it can take 16 minutes. Cryptosporidium could take up to 10 days to die off, but luckily it is uncommon in hot tubs – more likely to be found in public swimming pools.

This is another reason why it is essential to wait 20 minutes or more before entering a hot tub after sanitizing – you need to give the chlorine (or bromine) time to act.

You should shock your hot tub after heavy usage and at least once a week during normal use. Also, clean the filter to remove any contaminants.

This way, the chemicals act more effectively at keeping your water crystal clear.

Final Thoughts

There isn’t a simple answer to this question.

But at least you know that the important thing is to keep on top of your maintenance regime and check the chemicals regularly using test strips.

But as a general rule, wait at least 20 minutes with the jets on and cover off after adding any chemicals to your hot tub. Then dip a test strip in and check again. Depending on the levels and how much chlorine got added, you may have to wait as much as 24 hours or longer.

Don’t like waiting? Me neither.

That’s why my preferred method is to check the levels after soaking. I then adjust, leave the cover off for 20 minutes with the jets on, and then my hot tub will be ready (or close to it) the next time I’m ready to get in.

If there is anything I missed or if you have any questions on this subject, just drop me a line, and I will do my best to answer it. And don’t forget to check out the other related articles here on my site.

Just click on the links.

Photo which requires attribution:

Tub34 by Dave Stone is licensed under CC2.0 and was cropped, color-adjusted, and had a text overlay added.

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Jeff Campbell
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