Why Does my Hot Tub Use So Much Chlorine?

use so much chlorine lg

Have you noticed an increase in the amount of chlorine you have to add to your tub? You keep adding more, but it’s still not registering where it should on the test strip? If so, you’re probably wondering why does my hot tub use so much chlorine?

I know what the problem is, learned by trial and error:

Chlorine breaks down in heat faster than bromine and has to be added more often. This is why many prefer the latter for sanitizer. But having to add chlorine or bromine much more frequently than in the past may also reflect the presence of biofilm in the hot tub.

Biofilm uses up the chlorine faster and renders it less effective, necessitating the need for more.

But how do you know if it’s biofilm? Can you see biofilm in the water? Does adding more shock get rid of it? In this article, we’ll take a deep dive into why your hot tub is using so much chlorine.

Let’s dive right in…

How do you know if you have biofilm in your hot tub?

Biofilm build-up in a hot tub will be most evident when sanitizer and shock are having to be added much more frequently than in the past but still reading low on test strips. Biofilm is not typically seen and often resides in the plumbing.

Is there a film on the surface of your hot tub water?

Do the pillows feel slimy? Have you observed that it seems chlorine is “disappearing” from your hot tub water? You’ve got biofilm.

The chlorine levels are low because it’s trying to combat the biofilm, but the latter is a “tough customer”.

Biofilm is not an easy challenge to fix because the biofilm is a collection of microorganisms and bacteria that develop a protective layer that makes it hard for chemicals to reach the inner cells.

They attach themselves to the surfaces of the tub and the piping.

They are highly resistant to chemicals. So, even if you’re using more chlorine, for example, you might be surprised that the water is not easily restored to a healthy state.

Because it’s difficult to get rid of biofilm, it’s best to try and avoid its formation in the first place.

Biofilm thrives in moist environments. The plumbing of your tub is often a great host to these bacteria and microorganisms.

In effect, it’s a community of collaborative microorganisms and bacteria in a protective covering of slime.

Slime, cloudy, smelly, foamy water, and high chlorine usage are signs that you’ve got biofilm.

How do you get Folliculitis out of your tub? Check out a recent article of mine where I shared some effective strategies.

Just click the link to read it on my site.

What does biofilm look like in a hot tub?

Biofilm is a dark-colored slimy substance. At first, because of its microscopic nature, it may be invisible, but in time, if untreated, slime will be evident on the surface of the hot tub shell.

As you know, you should not soak in a tub that is slimy.

Apart from the fact that a slimy tub is a slippery tub, which could lead to unpleasant accidents, biofilm harbors infectious microorganisms.

So, slime or a slimy feel or appearance is a sign of biofilm in a hot tub.

In addition to the above, if you’ve noticed a spike in the level of chlorine you’ve had to add to the tub, you’ve got biofilm.

There’s a high chlorine usage because the slime acts as a protective cover within which the microorganisms continue to thrive!

You’re probably wondering if it’s safe to soak in a tub with a high chlorine level.

That’s what I looked at in a recent article of mine. I explained that it’s not safe to soak in a tub with a chlorine level above 3 ppm. But what really surprised me was how certain conditions could actually require medical treatment.

Just click the link to read it on my site.

How do I get rid of biofilm in my hot tub?

The best way to eliminate biofilm from a hot tub is to use a biofilm removing chemical and then drain, clean, and refill the hot tub.

In truth, I do a biofilm clean out every time I drain and refill my hot tub, which is about every 3 months.

The product I use and recommend is Oh Yuk Healthy Hot Tub Cleaner on Amazon. It’s got hundreds of reviews on Amazon, and almost all are 5-stars.

First, I take out my filters, then I just add about 8 oz of it to my water and turn on all the jets and water features with the cover off.

Then I let that run for 1 hour, restarting the jets as needed.

Then after an hour, I drain it, wipe it down with a mixture of water and white vinegar, and give it a quick rinse with the hose and wet/dry vac that up.

Then refill and treat the water as needed. And make sure to replace your filters after giving them a quick rinse.

How long should chlorine last in a hot tub?

As a general rule, chlorine sanitizer will last 2-3 days in a hot tub, provided that the hot tub is not infested with biofilm, which adversely affects chlorine efficiency. Increased usage and/or a larger number of people are soaking, may require additional chlorine.

You might think that 2-3 days is pretty short.

To have a healthy and sparkling hot tub water, chlorine (or bromine) has to be applied regularly. These are the sanitizers that purify the water and kill bacteria.

But the contaminants and bacteria multiply with use.

So, if a hot tub is being used frequently and by a lot of people, it would require a higher level of chlorine relative to one that’s only used now and then.

Ideally, you want to test the water before and after using the tub. Make sure you apply sanitizers after each use.

For more info about why your chlorine disappears, check out a recent article of mine, where I explained that chlorine breaks up faster in heat and that a biofilm buildup can reduce your chlorine levels drastically.

Just click the link to read it on my site.

What lowers chlorine in a hot tub?

Higher water temperatures, sunlight, biofilm buildup, and the presence of contaminants are the biggest factors that lower chlorine in a hot tub.

Sunlight’s UV rays could cause the chlorine levels to drop. Biofilm buildup exhausts a higher rate of chlorine, and contaminants bond with chlorine to form chloramines, reducing the chlorine level.

It’s helpful to ensure that your tub is covered when not in use.

Being under some shade is good too, because direct exposure to the sun’s rays, though lovely on the skin, actually lowers the chlorine level in the tub.

A biofilm is a group of microorganisms that employs slime as a cover and protective mechanism. They are highly resistant to chlorine, so you’ll most likely be using a lot more if you have a biofilm buildup.

As chlorine dissolves in your tub and gets mixed with water, it becomes hypochlorous acid.

It’s this acid that reacts with and kills the bacteria. But in the process, a reaction occurs between it and other substances in the water, and it becomes deactivated! This is why chlorine replenishment is an ongoing task.

What would happen if the chlorine level is too low?

I explored the theme in a recent article of mine. When the chlorine level is too low, bacteria and other harmful contaminants flourish in the water, making it unsafe.

Just click the link to read it on my site.


We explored how to know when you’ve got a biofilm buildup, what biofilm looks like, and how to get rid of it.

It’s a slimy and gross-looking group of microorganisms that attaches itself to the surfaces of moist environments. It’s host to infections. As such, it’s an issue that must be fixed asap.

We checked out proven ways to get rid of biofilm, such as ensuring the filters are clean, hyper-chlorinating, and refilling the tub after a thorough wash.

We looked at how long chlorine is supposed to last, and we wrapped up by looking at some factors that lower chlorine in hot tub water.

Photo which requires attribution:

Still frame taken from video How to Add Hot Tub Chemicals to your Hot Spring spa – by The Hot Tub Store is licensed under CC2.0 and was cropped 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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