What Happens if the Chlorine is Too Low in a Hot Tub?

All of us have done it. We go to get in our hot tub, check the water with a test strip, realize the chlorine or bromine levels are too low and get in anyway. So, what happens if the chlorine is too low in a hot tub?

Here’s what I’ve learned in owning 4 of them:

When chlorine or bromine levels are too low in a hot tub, it can allow bacteria and other harmful contaminants to grow in the water, potentially making it unsafe to soak in.

But while arguably the most important, those aren’t the only reasons.

In this article, I’ll discuss what to do if the chlorine is low in your tub and if it’s safe to soak in it that way. I’ll explain what to do if your chlorine levels keep dropping and tell you exactly how often you should add chlorine to your tub.

Lastly, I’ll reveal the best chlorine for hot tubs. Keep reading to find out more!

What should I do if the chlorine is low in my hot tub?

Adding chlorine shock to your spa is the fastest way to raise your chlorine levels. Shock is ideally added weekly to a hot tub which serves to reactivate the chlorine levels from the sanitizer.

But, sanitizer (chlorine or bromine) should be added a few times throughout the week.

Maintaining the right chlorine level is crucial to a safe hot tub experience. Chlorine or bromine is what protects you and your hot tub from harmful bacteria, fungi, and other microbial organisms. These can lead to skin irritation and disease.

Chances are the standard chlorine sanitizer you used is being overwhelmed by the number of contaminants it has to fight against. Or you simply aren’t adding enough of it, or frequently enough.

Shock can be chlorine and non-chlorine. But I prefer a chlorine shock in conjunction with bromine tablets in a floater for sanitizer. For me, that gets me crystal clear water with a low chlorine smell and no burning eyes. 

When using a chlorine shock, the chlorine levels will rise above the recommended amount (approximately 5 times), so you must wait at least 30 minutes for it to reduce to a normal level naturally.

The hot tub cover must be off, and the jets of your spa must be turned on.

The reason is that high levels of chlorine can corrode your spa. A handy tip is to shock your tub after sunset as the chemical will be most effective when not exposed to UV rays.

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

Low chlorine levels are dangerous to anyone soaking in a hot tub as this can allow bacteria and viruses to grow in the water. It can also lead to biofilm buildup inside the hot tub’s plumbing, and that can stay there even when normal chlorine levels are restored.

Think about it, all the lotion, natural oils, and sweat from your skin are released in the hot tub when you take a soak. If there’s not enough sanitizer-chlorine in the spa, the water becomes a thriving breeding ground for harmful bacteria.

I’m talking about itchy skin and eyes, rashes, and possibly, even a disease. Pseudomonas folliculitis is one of the harmful bacteria that may thrive in your hot tub water if you have low chlorine.

Aside from the danger to your body, low chlorine is also not safe for your hot tub. It will most likely damage it in the long run.

Now you know the consequences of low chlorine, here’s my recent article on what’s worse, high chlorine. I’ll cover how too much chlorine will affect you and your spa. I’ll also discuss how to check and lower your chlorine levels.

Click that link to read it on my site.

Why do my hot tub chlorine levels keep dropping?

If you find that chlorine levels are continuously low despite adding it frequently, the issue is most likely biofilm buildup inside the hot tub’s plumbing. This destroys chlorine levels quickly and requires it to be added more frequently.

I’ll assume that you’ve already tried dumping more and more chlorine in your hot tub, yet the chlorine levels keep dropping. Save that last capful and follow these tips.

How to get rid of biofilm

Biofilm is a slimy buildup caused by bacteria. It causes the seats and pillows of your spa to feel slimy, and the surface of the water gets a film. But more often, it gets into your plumbing, so you’ll need to clear them out.

Biofilm is resistant to chlorine, and that causes your chlorine levels to keep dropping. To fix this, you’ll need a hot tub cleaner, and I highly recommend the Oh Yuk Healthy Hot Tub Cleaner Gallon from Amazon.

I use that every time I drain and refill my hot tub (every 3 months).

After removing my filters, I pour in about 8 oz and turn on all jets and water features. Then I let that run for 1 hour, restarting the jets as needed.

Then I simply drain, rinse, and refill, and the biofilm is gone!

How the sun can lower chlorine levels

If your hot tub is overexposed to UV rays, chances are it’s causing your chlorine levels to drop quickly.

After all, the sun and heat destroy chlorine quickly. That’s actually why I prefer bromine sanitizer instead of chlorine.

Make sure you keep your hot tub cover secured whenever the spa is not in use. Many hot tub owners prefer to use bromine instead of chlorine for its resistance to sunlight. That being said, you’ll need to add shock to the water weekly to prevent it from turning into chloramines.

Ready to switch? Here’s my recent article on using a bromine sanitizer and a chlorine shock. While it’s totally OK to use chlorine shock and bromine sanitizer, it’s NEVER ok to mix chlorine and bromine sanitizer. And if you decide to change chemicals to sanitize, should you drain the water first?

Just click that link to read it on my site.

How often should you add chlorine to a hot tub?

Chlorine sanitizer should be added to a hot tub 3-4 times per week, depending on usage. Chlorine shock should be added weekly. But extra heavy usage may require additional sanitizer and shock.

So the answer to this really depends on how often you use your hot tub. The people using it also affect it. For example, if everyone soaking wears a lot of body lotions, perfumes, or skincare products, you will likely find it necessary to add it more often.

Additionally, in-ground spas that don’t have a lid will also require more frequent chemical use.

Bacteria can easily build up in your hot tub water, and the more bacteria present is, the faster the chlorine turns into chloramines. Chloramines still register on your test strips as chlorine but don’t actually protect the water from contaminants.

This is why chlorine or non-chlorine shock is important.

You should add shock at least once a week, so it recharges the existing chlorine. You should always test your sanitizer levels before and after adjusting the chlorine.

While chlorine and bromine sanitizers keep your hot tub clean and safe, you shouldn’t use your hot tub immediately after adding them.

Here’s my recent article where I discuss how soon you can use your hot tub after adding chlorine or bromine. After all, there are some cases where it’s advisable to wait up to 24 hours before entering. But the way I do it, I can get in almost immediately.

Just click that link to read it on my site.

What is the best chlorine for hot tubs?

The best chlorine for your hot tub is the Clorox all-in-one sanitizer, which acts as both a sanitizer and shock. It kills bacteria, keeps hot tub water clear and pristine.

It’s rated almost 5 stars on Amazon with over 1000 reviews. It’s also ranked #7 in Swimming Pool Clarifiers and Enzymes.

CLICK HERE to check the current price on Amazon.

It is also great for new hot tub owners who might be a little confused about using both chlorine and shock separately. It also saves time on maintenance.


This article covered what you should do if chlorine levels are low in your hot tub.

I also talked about the dangers of using a hot tub with low chlorine levels. I also covered reasons why your chlorine levels could be dropping and shared solutions. I went into detail about how often you should add chlorine to your hot tub.

Ultimately, proper sanitizer and shock levels are critical to your hot tub being safe to soak in.

So don’t neglect it! I like to check my levels after each time I soak and adjust if needed. That way, it’s more apt to be ready the next time I get in.

Photo which requires attribution:

ahhsome-filter-biocleaner-gunk-dirty by William Leonard is licensed under CC2.0 and was color adjusted, stretched, and had a text overlay added.

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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