Why Does the Chlorine in My Hot Tub Disappear? (& how to fix it)

Nothing is more frustrating than wanting to have a relaxing soak in your hot tub, but being unable to because the chlorine levels are low. So that has left a lot of hot tub owners to ask why does the chlorine level in my hot tub disappear?

Here’s what I know after years of owning them:

Chlorine levels can disappear in a hot tub for a few reasons. First, it breaks down in heat fast. That’s why many hot tub owners prefer bromine. But it also requires a weekly shock to keep it from turning into chloramines. Lastly, you may have biofilm buildup which can drastically lower chlorine levels. 

But that’s just the beginning!

Testing your hot tub’s water and finding out the chlorine is low can be frustrating and annoying. This is especially true if you’ve just put chlorine recently!

Maybe your hot tub’s chlorine level is dropping for no apparent reason. Or maybe it is too low, and you are wondering if you can still use your hot tub if it has a low chlorine level.

Keep on reading to find out why your hot tub’s chlorine level is so low.

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.

Why does my hot tub lose chlorine?

Is your chlorine level down low the next day after adding chlorine to your hot tub?

Are you getting frustrated that you have to keep adding chlorine day after day? It can get expensive but don’t worry, you can fix the problem!

Losing chlorine is a very common issue in hot tubs that may have biofilm build-up in the plumbing and jets. Biofilm is a group of microorganisms such as bacteria, fungi, and protists.

Biofilm and other organic contaminants can gain a foothold deep inside the plumbing of your hot tub. It’s harder for your sanitizer to clean this biofilm out. Your sanitizer is used up and wasted trying to kill and remove this biofilm.

Evidence suggests that high sanitizer levels are not capable of penetrating and removing this build-up, but people are unaware of this and keep trying to use sanitizers to clean this.

You need to use a product designed to purge or flush out your hot tub’s plumbing and help penetrate and disrupt the accumulating biofilm.

The best product out there for this is Oh Yuk Healthy Hot Tub Cleaner (click to see the current price on Amazon). In fact, it has some of the best reviews of any hot tub product on the market. Free Prime shipping too.

Just add 1 cup and turn on the jets for about an hour. Then drain the hot tub, wipe it down, and refill.

Most people find that they don’t have to use as much sanitize or as often once they do this. Plus, your water will feel, smell, and look better than ever.

Do this every time you drain and refill your hot tub.

Not sure how often you should be draining and refilling your hot tub? Luckily, I break that down in a recent article. It’s not a simple answer either as the size, usage, and the number of people who are typically in your tub can affect the frequency.

Just click that link to read it on my site. I even cover how I drain my hot tub in as little as 15 minutes!

How long does chlorine last in a hot tub?

When chlorine in a hot tub is dissolved in water, it creates hypochlorous acid which reacts with bacteria in the water.

It breaks bacteria down and kills them in the process. During this process, the hypochlorous acid molecules (chlorine) will react with other elements in the water and become deactivated. This is why constant maintenance of your hot tub is required.

For daily use, a chlorine level of between one and three parts per million must be maintained in your hot tub at all times. The amount of chlorine needed can change, depending upon your usage and soaking habits.

Too little chlorine in your spa will allow bacteria to grow.

Too much chlorine can irritate anyone who soaks in the hot tub, causing red and itchy eyes and skin. It can also potentially damage some hot tub parts. Adding chlorine to your water every other day will keep your spa water within range.

The time it takes for chlorine to last in your hot tub depends on the amount you use, and how frequently you bathe. But I will say that because heat destroys chlorine faster than it does bromine, some hot tub owners prefer bromine.

Think bromine might be better for your hot tub than chlorine?

You might be right! Luckily, I break down the difference between bromine and chlorine in this recent article. I give you all the pros and cons for both, including which one holds up to heat better and which is cheaper in the long run.

Just click that link to read it on my site.

How do you fix low free chlorine in a hot tub?

On a test strip, there is a reading for both Total Chlorine and Free Chlorine.

Let’s understand these terms first. Total chlorine is free chlorine + combined chlorine. Free chlorine is chlorine that isn’t combined with anything else. It is free and can be used as an effective sanitizer.

Combined chlorine, also called chloramines, is chlorine that is bonded or attached to anything it was working on.

Free chlorine will quickly turn into combined chlorine if your hot tub’s water has unwanted bacteria or disease. This will make your chlorine reading low.

If you are smelling a strong chlorine smell, it means that you are likely smelling chloramines.

This means your hot tub is experiencing hot tub “lock”. This means that your hot tub is not being sanitized correctly by your chlorine. This confuses many hot tub owners as it smells like there is chlorine.

The test strips also show correct chlorine levels. But you aren’t being protected by free chlorine.

This is why shocking your hot tub weekly is needed. Shocking a spa means applying a dose of chlorine (sodium dichlor) or non-chlorine shock (potassium monopersulfate or MPS).

One reason for this treatment is to break-down organic waste contaminants which cause odor and cloudy water. When chlorine “lock” happens, shocking the hot tub will break apart the chloramines and purify your hot tub water.

Hot tub shock confuses a lot of people.

Is it the same as oxidizer? How often should you apply it? An can you use a chlorine shock with bromine or a non-chlorine shock?

Luckily, I cover all you need to know in a recent article. There I get into all of that in simple terms to break down exactly what’s best for you. That way you can stop reading and get to soaking!

Just click that link to read it on my site.

Is it safe to go in a hot tub with low chlorine?

It is absolutely not safe to soak or bathe in a hot tub with low chlorine levels.

Bacterial levels in hot tub water start to rise and make them unsafe when chlorine levels are low. Certain bacteria in hot tub water thrive off of low sanitization and hot water.

Unpleasant or dangerous bacteria like pseudomonas folliculitis are highly contagious and infect the skin of people with poorly sanitized hot tubs.

Anyone who soaks in a low chlorine level hot tub may have to deal with nasty bacteria or disease. They may also get red, itchy, and dry skin, in addition to itching or burning eyes and nose.

Additionally, low chlorine levels in hot tub water can turn the water cloudy. This gives the water an unpleasant look and can take a couple of treatments to get rid of.

Low chlorine levels may also cause corrosion of metal hot tub parts like your heater element, in addition to staining due to the metal corrosion.

To avoid these situations and issues that come with them, it is a good idea to frequently check the chlorine, pH, and alkalinity levels in your hot tub. Use a test strip to do this.

Curious about using a hot tub with a high pH level?

That’s not great either. So check out this recent article where I break down some of the worst aspects of a high pH including what it can do to your equipment.

Just click that link to read it on my site.

How do I raise the chlorine level in my hot tub?

The first step in figuring out why your sanitizer is low is to determine if there are problems with either establishing a sanitizer level or maintaining the level.

If the issue lies within getting the sanitizer level to the required range, then you must shock your hot tub with an oxidizer.

I shock my hot tub using a chlorine shock once a week. But non-chlorine shock works fine too.

The next most common question people have is about how soon you can enter your hot tub after adding sanitizers or shock?

Luckily, I’ve done the research there too in one of my recent articles. Depending on the chemicals you’re using that can be as soon as 20 minutes. Others may require you to wait up to 2 hours.

So just click that link to read it on my site.

If you prefer to “set it and forget it” you can also consider a floating dispenser.  

I love the FROG @ease Floating Sanitizing System (click to see it on Amazon). It’s so easy you may wonder why you didn’t get one years ago!

Here’s what I love about it:

  • An Amazon’s Choice product
  • Great reviews
  • Only requires you to shock once a month
  • It is much smaller than typical floaters so it won’t get annoying
  • It automatically rotates when it’s out of sanitizer
  • Uses 75% less chlorine
  • Lasts about 4 weeks for the sanitizer cartridge
  • The mineral cartridge lasts 4 months!

So definitely check out the FROG @ease Floating Sanitizing System on Amazon and see if it’s not perfect for you!

Use as much chlorine or bromine that is necessary to keep 1-3 parts per million of your sanitizer of choice, depending on the number of people soaking and how often you use the hot tub.

Did I cover all you wanted to know about why the chlorine levels in your hot tub may be dropping?

Losing chlorine is a common issue in hot tubs that may have to do with biofilm being built-up in the plumbing and jets. Biofilm is a group of microorganisms such as bacteria, fungi, and protists.

It’s hard for your sanitizer to clean this biofilm out. Use a product designed to flush out and kill the stubborn biofilm that is in your pipes. The best one I’ve found is Oh Yuk Healthy Hot Tub Cleaner (click to see the current price on Amazon).

To figure out why your sanitizer is low, first determine if there are problems with either establishing a sanitizer level or maintaining the level.

A chlorine level of between one and three parts per million must be maintained in your hot tub at all times. If your total chlorine is high but your free chlorine is low, you will need to shock your hot tub.

Photos which require attribution:

PineapplePoint1.JPG by Ed and Eddie is licensed under CC2.0


Jeff Campbell

Jeff Campbell is a husband, father, martial artist, budget-master, Disney-addict, musician, hot tub lover, and recovering foodie having spent over 2 decades as a leader for Whole Foods Market.

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