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Does Chlorine Raise pH in a Hot Tub?

By: Author Jeff Campbell

Posted on  - Last updated:

Categories Hot Tub Water Chemistry

So, you’ve got the alkalinity and the pH right, about to add the chlorine, and now you’re thinking, “does chlorine raise pH in a hot tub?”

At normal levels, adding chlorine will not affect the pH of the water in a hot tub. However, adding too much chlorine can reduce the pH. So always add all chemicals in small amounts, wait 20 minutes, and test again.

You can always add more. You can’t add less.

So in this article, we’ll get into how to know exactly how much to add, how much high levels of chlorine will affect the pH, and what to do if you do get the pH out of whack.

Let’s get into it!

Ready to Spend Less Time On Maintenance and More Time Enjoying Your Hot Tub?

Let’s face it. Balancing the water, cleaning filters, dealing with rashes, and trying to figure out which chemicals to buy and add can make you feel more like a chemist than someone who just wants to relax after a long hard day!

That’s exactly why The Hot Tub Handbook and Video Course is so valuable!

This is from Matt over at Swim University and he developed it for people looking to save money, time, and frustration. His tips on chemicals can save you $100/year just by making sure you buy only what you need.

So if you’re ready to stop being confused or frustrated with your hot tub and start spending more time in it, check out The Hot Tub Handbook and Video Course.

Just click that link to learn more on their website.

chlorine raise pH lg

Does high chlorine cause high pH in a hot tub?

Chlorine in powdered or liquid form is naturally alkaline, so adding chlorine does increase the pH in a hot tub slightly. However, because chlorine also reacts with the water to form hypochlorous acid, this tends to reduce the pH. The net effect is no change.

The problem arises when you add too much chlorine, and excess hypochlorous acid is formed.

This will reduce the pH in your hot tub. Perhaps more significant, high chlorine levels will reduce total alkalinity, making it difficult to control the pH.

Never use chlorine to adjust pH in your hot tub. There are other chemicals you should use for this purpose. Chlorine’s job is to disinfect.

And if you just need to bump the pH up a tad, try just running the jets. Jets naturally aerate the water and will naturally increase the pH slightly with no chemicals needed.

Ideally, chlorine should be between 3 and 5 parts per million (ppm). 

As a guide, if you have a 500-gallon hot tub, that’s around 2/4 ounce or 3 teaspoons of chlorine granules every 2 or 3 days.

Or you may prefer using chlorine tablets if you’re not sure how much to add. These come in measured doses that dissolve over time.

Always use the 1” tablets that are specifically designed for hot tubs, not the 3” swimming pool tablets.

You can put these tablets in a floating dispenser such as the Aquatix Pro Pool on Amazon. This thing is dirt cheap and has almost 2,000 near-perfect reviews!

Click on the link to check the latest price.

What causes hot tub pH to go up?

The number one cause of high pH in a hot tub is high alkalinity (above 120 ppm). For this reason, it’s always best to balance the alkalinity first and then the pH.

But there are several causes of high pH in a hot tub.

Many people get confused about pH and alkalinity, particularly as pH is a measure of acidity, from highly acidic to highly alkaline. But total alkalinity, which is what we’re interested in, is a measure of the amount of dissolved alkali in the water.

If the alkalinity is too high, the pH level will rise as well.

You can find out more about this in a recent article. What really surprised me was how one affects the other, and there’s only 1 way to really affect one without the other.

Just click on the link to read it on my site.

Another cause of elevated pH levels is a buildup of carbon dioxide under the lid. This occurs when you run the jets with the cover still on, creating a lot of bubbles and the heat of the water generates CO2.

When CO2 dissolves in water, it creates carbonic acid, which will lower pH, but when the water becomes agitated by the jets, the carbonic acid disburses, causing the pH to rise.

This is normal and one reason why you should constantly check the chemical balance of the water in your hot tub.

What happens if you put too much chlorine in a hot tub?

High levels of chlorine can irritate skin and eyes, and if the level is above 5 ppm, it can cause nausea, headaches, and breathing difficulties. But high levels of chlorine can degrade the surfaces of the shell and accessories such as headrests, as well as the pipes, pump, and heater.

(source)

High chlorine levels can also lead to false pH readings, so you must get this right.

If you choose to use chlorine as your hot tub sanitizer, you’re not alone. It is by far the most popular product to use for several reasons.

But how much to add, and how often are 2 of the questions I get asked the most.

To find out more, check out this recent article. Too much chlorine is just as bad as too little. And there’s 1 crucial thing to know if you choose chlorine over bromine for your sanitizer.

Just click that link to read it on my site.

So how much should you add? Just over half a teaspoon per 100 gallons every 2 or 3 days should be enough, but always test and add more if necessary. For the average large hot tub, that will be about 3 teaspoons every few days.

The level of chlorine in your hot tub water should not exceed 5 ppm and not drop below 3 ppm.

You should shock your hot tub after heavy usage and at least once a week during normal use. This is the process of adding a larger dose of chlorine – between 11/2 to 2 teaspoons per 100 gallons – to the water, increasing the available free chlorine, and reactivating the sanitizer.

And as with adding any chemical, leave the lid off, and the jets on and then wait at least 20 minutes and test again before getting in.

What happens if the pH level is too high in a hot tub?

Using a hot tub when the pH is high can lead to dry, itchy skin and cause the eyes to sting. But high pH levels also reduce the efficiency of chlorine as a sanitizer, requiring more to be added than usual.

High pH also leads to hard water that causes several issues:

  • foam
  • musty or stale odor
  • scale buildup in pipes

But how high is too high to use?

I wrote about this in a recent article. If the pH is high, that is above 7.8 ppm, give the hot tub a miss until you get it back down again. But there’s 1 trick to get the pH down quickly.

Just click that link to read it on my site.

The pH of your spa water must stay within the range of 7.2 – 7.8. Any fluctuations above or below this range can cause spa water to be corrosive or scale forming.

Aluminum sulfate (AKA Alum) and sodium bisulfate (AKA sulfuric acid) are popular chemicals to reduce the pH level of the water in your hot tub.

Muriatic acid is also effective at reducing pH, but many hot tub owners prefer to use hydrochloric acid, which is weaker but less hazardous.

After adding any acid, you should wait between 4 to 6 hours before going into your tub to make sure it has dissolved. Otherwise, you run the risk of burning your skin.

Want all my chemical recommendations?

Just CLICK HERE to go to my page of recommended products to see what I personally use.

Will adding bromine lower pH in a hot tub?

As bromine pH is neutral, it will not lower the pH in a hot tub and will have very little effect up or down on the overall pH. 

Bromine does work well as a sanitizer though, but you should never mix it with chlorine. The chemical reaction can give off toxic fumes.

Despite the popularity of chlorine, bromine is actually more effective at sanitizing the water in your hot tub because it is more stable than chlorine at high temperatures.

Bromine is very effective at killing off viruses and bacteria.

Bromine dissolves much slower than chlorine, but it is less harmful to the skin and eyes, so you can use your hot tub within 15 minutes of putting it in. You need to maintain a level of 4 to 6 ppm, so you need to add more than you would chlorine, but less often.

The downside is it is more expensive than chlorine. But because you don’t have to add it as often, the cost is really a wash.

However, if you are allergic to chlorine, I don’t think bromine will be any better for you. Bromine is chlorine-based, so you may have to look at other alternatives such as saltwater.

Bromine can be added in the same way as chlorine – either granules, liquid, or tablets – and you can use a dispenser, but don’t use one that has had chlorine in it without rinsing it out first.

Final Thoughts

From this, you will see that chlorine doesn’t raise the pH in a hot tub. If anything, it will lower it, but only if you put too much in.

I hope this covered everything you wanted to know. Just remember to keep the chlorine level between 3 and 5, and you won’t go far wrong.

If there is anything I missed, or 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.

Ready to Spend Less Time On Maintenance and More Time Enjoying Your Hot Tub?

Let’s face it. Balancing the water, cleaning filters, dealing with rashes, and trying to figure out which chemicals to buy and add can make you feel more like a chemist than someone who just wants to relax after a long hard day!

That’s exactly why The Hot Tub Handbook and Video Course is so valuable!

This is from Matt over at Swim University and he developed it for people looking to save money, time, and frustration. His tips on chemicals can save you $100/year just by making sure you buy only what you need.

So if you’re ready to stop being confused or frustrated with your hot tub and start spending more time in it, check out The Hot Tub Handbook and Video Course.

Just click that link to learn more on their website.

Photo which requires attribution:

Still photo taken from video How to add start up Chemicals to a Bullfrog spa Hot Tub by Best Hot Tubs and Spas is licensed under CC2.0

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Jeff Campbell
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