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Hot Tub Sanitation

Jul 25, 2018 | Hot Tub Water Quality

There are several ways spas, hot tubs, swim spas and pools are kept clean and sanitary. Over the years the debate as to what are the best hot tub sanitation methods is always a hot topic for discussion and the debate is likely to continue on until something new and revolutionary comes along.

Before we dive into each individual system, there is one thing we need to make clear. There is no sanitation system currently on the market that can completely replace or eliminate the need for common sanitizers like chlorine or bromine.

All hot tub sanitation methods have their pros and cons and probably the most common method of keeping spas and hot tubs clean are the use of chemicals such as chlorine and bromine. Salt units, ozone and ultraviolet light is also used to purify water as additional hot tub sanitation methods.

Both chlorine and bromine are very good at what they do. Both will sanitize your spa and keep your water clean. You may have your own personal preferences. If you forget to regularly add sanitizer to your hot tub or if you want to try and save a little money on maintenance, then chlorine may be the way to go. If your skin is sensitive, bromine would be the better choice, but it is a little more expensive.


Chlorine is considered one of the more cost effective and fast acting sanitizers you can use for hot tub sanitation. If you are looking to clean a hot tub fast without spending a lot of time on maintenance, chlorine will likely be the better way to go. It doesn’t break down as fast from the sun as does bromine, but you likely will need to add stabilizer to the hot tubs water. However, a lot of hot tubs are not in direct sunlight all day, so this may not be an issue.

Because chlorine has a rather high pH value to it, you will have to watch the water balance if you regularly use chlorine, and you may need to add pH decreaser to the spa water. Chlorine is known to cause some irritation to people with sensitive skin. Chlorine also has a fairly strong chemical smell which can be an irritant when levels of concentration are not correctly maintained.


Bromine may be a little more expensive and a little slower to react than chlorine, but overall it can do a better job of killing algae, bacteria and other contaminants for a much longer time, especially in warm water environments like a spa or hot tub. Of all the contaminants, it does a really good job of destroying bacteria and viruses.

Bromine has a pH value that is much lower than chlorine, so you won’t have so much of a chemical balance issue to deal with that you get when you use chlorine. Another plus, it doesn’t have as strong of a chemical smell to it, as chlorine may have.

On the other hand, it is more expensive, so your maintenance costs can go up if you choose to use bromine. Also, this chemical is harder to completely wash off your skin in a shower after you have spent some time in a spa or hot tub. Although it can also cause skin irritation, it is usually much easier on your skin compared to chlorine.

Ultra Violet Light (UV)

hot tub sanitation unit

The first alternative sanitizer solution we are going to look at is UV, or ultra violet light systems, example unit shown above. We all know pretty much what UV light is, those rays from the sun that give you that sweet summer tan. Well, there are many frequency spectrums of UV light and certain spectrums of UV light are very destructive to living organisms.

The important thing to understand about UV is that it does not really kill anything. Instead the UV light scrambles the organisms DNA causing it to be inactive, which means it can’t reproduce. This makes any bacteria or virus that comes in contact with the UV light harmless.

The one downside of UV is its limitation to only a certain frequency of the UV light spectrum. There are a lot of things that can disrupt the spectrum of light from contacting the organisms in the circulation system, something as simple as dust on the bulb itself can render the UV sanitation system pretty much useless.

Also, sanitation relies on direct line of sight so the organisms are only destroyed when they come in direct contact with the UV. The circulation system in the hot tub makes it so eventually all the water (and whatever is in the water) does get exposed to the UV light multiple times of day. However, this fact of direct contact is why there needs to be some level of residual sanitizer in the water at all times.

Ozone Sanitation Systems

hot tub sanitation unithot tub sanitation unit

Ozone gas sanitation systems have been around in the hot tub industry a little longer than UV type systems. When you think of ozone you usually think of the layer above our heads in the sky that protects us from UV radiation. However, ozone gas or O3 is a powerful oxidizer, and has been used in many commercial and residential applications including hot tub sanitation for quite some time.

It is such a powerful oxidizer that it can oxidize and destroy any bacteria or pathogens it comes in contact with. The key there is WHAT IT COMES IN CONTACT WITH. Hot tub manufacturers design the ozone system so that the O3 gas is injected into the plumbing system and mixes with the circulated water. So as the pump is moving the water through the system it ends up mixing with the O3 gas and any particles or contaminants that it comes in contact with get oxidized and killed.

The other nice thing about ozone is that it can oxidize chloramines and bromines, which are the bad smelly irritating byproducts of chlorine and bromine. With a bromine sanitizer it actually turns used-up bad bromine (bromines) back into good use-able bromine, freeing it so it can sanitize the water again. Ozone is used in homes and hot tubs to kill bacteria in the water and to reduce the amount of chlorine or bromine required by reactivating them to their free state. Since ozone does not remain in the water long enough, ozone by itself is ineffective at preventing cross-contamination among bathers and must be used in conjunction with halogens (chlorine or bromine).

Salt Water Sanitation

hot tub sanitation systems

The biggest misnomer about salt water sanitizer systems in pools or hot tubs is that the water is chlorine free. People think that because they use a salt generator that they don’t have chlorine in the hot tub pool water. However, a salt generator breaks the salt in the water down to chloride and sodium so you have chlorine in the pool generated by the breakdown of the salt in the water providing hot tub sanitation.

What a salt generator does is splits salt into chlorine which immediately turns into hypoclorus acid, which is the strong sanitizer found in swimming pools and spas. It has the same exact effect as pouring liquid chlorine or bleach into the water, except in the case of a salt generator you are making your own chlorine.

When you have a salt system in your hot tub you eliminate the need for external chlorine granules or bromine tablets to maintain a sanitizer residual. However other water balancing chemicals are still needed in order to maintain the water clarity, the spa equipment longevity and hot tub sanitation.

Bottom Line

The best part about the previous systems, UV and Ozone is that you are able to lower the amount of chlorine or bromine needed in a pool or hot tub to keep it clean. In a pool or hot tub with a salt system, it is all chlorine and you maintain a higher residual chlorine level than what is needed with ozone or UV systems.

The other downside of salt water sanitation is its corrosiveness to metals and other components in the hot tub. This is why it is very important that the water chemistry balance is kept perfect at all times with a salt generator as the system is very sensitive. This just means the water will need to be tested and adjusted a bit more than a non-salt system. Also, the salt generator tends to push PH levels in the water up, and as PH rises chlorine becomes a less effective sanitizer so use of acid or granular PH down is needed regularly.

What’s The Best System For My Hot Tub

I get asked this question all the time, but the answer is not always simple. There are a number of factors I consider when recommending a sanitation system for a customer building their own hot tub. Water volume being treated is my first consideration and followed by that is, are any of the bathers using the hot tub prone to skin sensitivities or maybe allergic to certain chemicals. The answers to these first two questions will be the primary factors for selecting the hot tub sanitation system for their hot tub project.

I’ve used over the counter chemicals, salt units and an ozone system in my own hot tub. My personal preference is the Ozone system. I do add maybe a table spoon of chlorine granules every other day to maintain free chlorine levels. And I do use a higher output ozone unit because my filtration system does not run 24/7 like many of those portable spa systems do. My water stays crystal clear and clean without any unwanted smells.

I hope you have found this information informative and useful for whatever sanitation system you select. And as always, if you have any questions that I can help you with, feel free to contact me.

Gene Trumbull
Custom Built Spas

Call With Questions (860) 571-8440



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