What is a Hot Tub Sanitizer and Which Sanitizer is the Best?

Posted by

A hot tub sanitizer kills bacteria and purifies the water. The sanitizer is the most critical component to a healthy hot tub experience.
Hot Tub Sanitizers

The Center for Disease Control only recommends a few sanitizers as proper hot tub disinfectants, or “Primary Sanitizers”. These include: chlorine, bromine and a few mineral sanitizers when used in combination with an oxidizer.

Other products that do help destroy microorganisms but are not effective enough to use alone are “Secondary Sanitizers.”

UV is not a primary sanitizer.

Ozonators are not primary sanitizers.

Oxidizers aka non-chlorine shock or MPS are not primary sanitizers.

UV, Ozone and oxidizers can be noted as chemical reducing aids, but still require the use of a halogen based or primary sanitizer.

There are many sanitizers on the market. Some are great, some are mediocre and some are terrible. Below, I’ll take you through the different sanitizing options and the pros and cons of each.


Chlorine is the most widely used sanitizer for pools. Because it does not come in tablet form, it is not a suitable stand-alone sanitizer for spas, as the granules dissipate too quickly.

Chlorine is a great shock for hot tubs and is commonly used in conjunction with mineral sanitizers, burning off dead organic matter and preventing cloudy water.


Bromine is the most widely used hot tub sanitizer. It comes in tablets which can be inserted into a floating bromine feeder and provide continuous sanitation to the water.

While very effective at killing bacteria, some people may have a sensitivity to bromine. Some individuals experience dry or irritated skin and find the chemical odor of bromine to be overwhelming. Learn more about bromine.

Cons of Chlorine & Bromine

Excessive use of halogen sanitizers (chlorine or bromine) can bleach and damage the underside of the spa cover, fade swim suits and even pit the hot tub shell.


Mineral Sanitizers

There are a couple “alternative hot tub sanitizers” on the market that use copper or silver ions to sanitize spa water. Many people switch to mineral sanitizers because they are odorless, more natural, and do not fade swimsuits or damage spa covers.

  • Cleanwater Blue – Cleanwater Blue is an EPA registered liquid bactericide/algaecide made from copper ions. These ions disrupt the cell structure of microorganisms, eliminating them in a safe way. The science behind Cleanwater Blue dates back to ancient times, when drinking water vessels were made from copper to help keep the water fresh. While crossing the plains, American settlers often put copper pennies into their water barrels to prevent stagnation.

Cleanwater Blue Sanitizer

  • Nature 2 – Nature2 is an EPA Registered cartridge containing silver minerals, which you can put in your filter cartridge or in the filter housing. As water passes through the Nature2 cartridge, positively charged silver ions disperse in the water, and destroy negatively charged cells of microorganisms. Like Cleanwater Blue, this system is a great alternative for people who have a bromine sensitivity and is comparable in price.

Nature2 Mineral Sanitizer

Cons of Mineral Sanitizers

While there are no major cons to using mineral sanitizers, using test strips with these systems can be somewhat tricky. To date, there is no practical way for users to test silver ion content, so care must be taken to follow dosage instructions. However, copper test strips are available for the Cleanwater Blue system.

Bromine/Chlorine + Mineral Sanitizers

  • Spa Frog – Spa Frog sanitizing systems combine minerals and a small amount of bromine to achieve sanitization in hot tub water. By incorporating minerals, the amount of bromine needed is greatly reduced. Spa Frog systems are a great option for people that like the test-ability of bromine and the benefits of mineral sanitizers.

Spa Frog Mineral Sanitizer

  • PoolRX – Despite its name, PoolRX is a great mineral sanitizer for spas. This product works synergistically with a constant low level of chlorine.

Pool RX


Ozonators, or ozone generators, are add-on components in hot tubs that distribute ozone through the air lines. Ozone works to break down contaminants in hot tubs by oxidization, destroying bacteria, soap residues and other undesirable particulate on contact.  Ozone also frees up spent chlorine and bromine particles, enabling them to be reused again and again and allowing you to use far less chemicals to maintain sanitation.

Ozone has a very short half-life in water (about 15 minutes) and must be used in conjunction with a sanitizing agent, such as Bromine, Cleanwater Blue or Nature 2.
Aqua Sun Ozone

Cons of Ozone

Excessive ozone can cause damage to the underside of spa covers and thermal blankets.

Salt Systems

Saltwater based systems, such as the Saltron Mini, generate chlorine by passing a mild electric current through salt water. Salt, which is added to the spa water, is the source of the chlorine which acts as the sanitizer with this system.
Salt Systems

The ease of use with these systems makes them very popular. Many people also experience softer, more moisturized skin after soaking in a hot tub equipped with a salt system.

The low salinity level required with these systems does not corrode spa equipment. Learn more about salt systems.

Cons of Salt Systems

The cells which generate the chlorine require some cleaning maintenance.


Biguanide sanitizers are commonly hydrogen peroxide based and require proprietary companion water balancing products.

Cons of Biguanide Sanitizers

Biguanides are known to erode certain plastic components, such as jets, causing them to no longer stay in place. Biguanides and their proprietary companion components are significantly more expensive than most other sanitizing systems. Many people report coughing and burning sensations in the lungs and eyes after inhaling steam in hot tubs treated with biguanide sanitizers. Commercial Hydrogen Peroxide used in hot tubs can be dangerous to store, handle and transport. Biguanide sanitizers often fail to prevent algae slime.

Mystery Ingredient Systems

There are several mystery ingredient “water treatments” on the market which claim that you can “throw away all of your other chemicals” and “use this product and never test your water again”.

Silk Balance

Beware! These products survive by using irresponsible and dangerous marketing. The small print on these products state that they do not kill bacteria.  The truth is that these products are mostly comprised of dissolved salts in water. Truly not worth the $100+ price tag.

If it sounds too good to be true, it usually is.

So, Which is the Best?

It is clear that mineral systems are gaining huge popularity. Being that they are odorless, gentle on the skin and hot tub equipment, and comparable in price to chlorine/bromine sanitizing systems, it’s not hard to understand why.

Do you have questions about your hot tub water maintenance? Comment below for expert assistance!


  1. Hi Cd,

    Thank you for checking with us. No, you do not want to use Nature2 in a saltwater tub. Your saltwater system is already the sanitizer for your spa water, so adding the Nature2 would be a waste of your money.



  2. I have read your entire list of responses and I still do not know which system is best. It seems it boils down to the choice between the Frog System and Ozonators. So, straight forward, which is best?


  3. Hi Larry,

    Of these two choices, the Floating Spa Frog System is going to be the best option of sanitizer. This system contains mineral and bromine cartridges that are pre-filled and will need to be replaced when depleted. The bromine cartridge can be adjusted to meet your sanitizing needs of at least 1.0 ppm bromine level. This system is far easier to maintain than bromine tablets and with the mineral cartridge it uses 50% less bromine.

    An ozonator is not a standalone sanitizing system but works with bromine, Cleanwater Blue or Nature2 to improve the water by oxidizing organic and inorganic contaminants. Chemicals used are reduced by 50 – 75%, but are still necessary to purify the spa water.

    Regardless of choice, shocking the spa is recommended at least once per week or after each use to allow the sanitizer to perform at peak efficiency.

    I hope this helped you decide which sanitizer to choose. If you have any other questions, please let us know.



  4. I have an ion (silver) hot tub cartridge and use both the mps shock and occasionally the ‘up ph’ as the test stip suggests. However, lately we have been getting a lot of suds. We changed the cartridge, cleaned the filter and emptied and refilled the tub. What am I missing?


  5. Hi Judi,
    The suds could be from low pH and Alkalinity, or they could be cause by different lotions or soaps getting in the tub. If the pH and Alkalinity are at the right levels, you might try our Foam Free to get rid of the foam. Using a small amount of Dichlor (Chlorine granules) can also help, and is completely compatible with Nature2, and any other ion sanitizer.
    I hope this helps!


  6. Hi, I have a Sundance spa which uses a mineral cartridge(not currently in use). I’ve never had time to research it or use it until now and I’m very interested in using this method. I ordered a new Sundance cartridge and when it arrives I will change my water and start fresh. My question is about bromine – there is a warning that these cartridges aren’t compatible with bromine! So if this is the case will I also have to switch to chlorine as my additional sanitizer? I’ve read that chlorine doesn’t work well in spas so I’m concerned about how to use the mineral sanitizer correctly with chlorine and/or is the info about bromine and minerals is incorrect. Can you advise?


  7. Hi Frank,
    Thanks for checking with us! You’re right on almost all accounts. You cannot use bromine with the mineral sanitizer, that is true. You can use chlorine, and there is a granular chlorine that works great with mineral sanitizers. It’s called Dichlor, or Spa Sanitizing Granules. On our site you can search item codes CA1004 or CA1011, depending on which size you want. With a mineral sanitizer you want to add 1-2 tablespoons of Oxy-Spa (non-chlorine shock) after each use, and you can add about 2 teaspoons of Dichlor once a week, or as needed to clear up cloudiness. I hope this helps, and please let me know if you have any other questions!


  8. Just starting to read up on this for alternatives to what we are using. We have a Hot Springs Spa, about 3-4 years old. Have been using the Spa Guard Shock weekly with the Silk Balance and also have the mineral stick cartridge that we put in the filter that gets changed every 4 months….we add the shock and Silk weekly. The Silk has become so expensive I cannot justify using it anymore and am looking for an alternative. We put some Silk Balance in it yesterday and got a heavy yellow film on the top of the tub and it bubbled like bacteria. Skimmed it off, cleaned the filter and the water is slowly becoming un-cloudy but obviously we cannot use that. What is an alternative to the Silk Balance? We have done everything up to this point our tub company suggested but the cost is just becoming crazy. We grew up with swimming pools and it seems keeping those maintained with chemicals was far cheaper than our tub. Suggestions? Help? Thanks, Dave, Texas.


  9. Hi Dave,

    Great question! The Silk Balance is not a mandatory product and you can discontinue use right away. It’s sold as a water softener, pH stabilizer, and a whole host of other claims, but none of those are necessary for clean, clear water.

    To get that gross yellow scum (probably biofilm, a bacteria that grows in your plumbing), use Spa System Flush in your tub, then drain and refill. There are some other drain/jet cleaners but the SeaKlear Flush is by far the most effective.

    Additionally, your mineral cartridge and shock can be purchased for significantly less. The mineral cartridge is most likely made by the same company as the yellow one in this article, and the only differences between the two is the color of the plastic and the shape of the adapter piece that keeps it from getting sucked into the plumbing.

    The shock you are using weekly could either be dichlor or monopersulfate(MPS) or a blend. You are better off using the pure products without fillers, and adding the dichlor (chlorine) as needed and the MPS (non-chlorine) more frequently to deal with oil, lotion, dead skin, sweat and other stuff we leave behind in the hot tub.

    There are even very low cost, but very effective, additives that soften the water, keep pH in check and much much more! Choosing these additives individually means you aren’t buying or adding more chemicals than you need.

    I highly recommend you look online for products not branded by your dealer or manufacturer. I may represent an online hot tub supply store, but even if you don’t buy with Spa Depot, you will save tons of money and have more choices. Dealers can be great for quick stops in an emergency, but if you are looking to save online is your best bet by far.

    Let me know if you would like help creating a new maintenance routine, or if you have any other questions.



  10. I have purchased a new hot tub that has an ozone generator. I used the frog system in my old hot tub but it did not have an ozone generator. Is the frog system compatible with the ozone generator? If not, which sanitizer should be used? Easiest one please!!


  11. Hi Nancy,

    Thanks for reaching out to us about using an ozone generator. You’re in luck, ozone generators are compatible with the Spa Frog Sanitizing System! So you can continue using this system you’re most familiar with. Ozone simply reduces the need for chemicals, so you may see a longer usage period with the Spa Frog System.



  12. Based on your grid of benefits each sanitizing system offers- I am thinking of switching from Nature 2 to Cleanwater Blue (less expensive and test strips for the copper) I have recently refilled the hot tub and balanced the PH. I have used granular chlorine and Oxy Spa for a month. Can I switch to Clearwater Blue without draining this water?

    A completely different question- we have had this new hot tub for a little over a year and have had several episodes of what I think is white mold. We treated the last hot tub in the same manner and in 10 years never once had this problem. It is a MAJOR deal to get rid of it! I THINK it might be because the new tub has so many diverters that some lines are never on- and then when they are used- its there!! I would appreciate any suggestions you have.


  13. Hi Patrice,

    When switching to any new sanitizing system you’ll want to flush your hot tub plumbing system with Spa System Flush (https://www.spadepot.com/Spa-System-Flush-16oz-P817) then drain and refill the water.

    But first, I would suggest you follow these steps to determine if your episodes are white mold or simply excess calcium:

    1. Take a sample of the flakey water.
    2. Pour 20 drops of liquid bleach into the water sample, gently stir and wait 30 minutes.
    3. If flakes are still there, it’s more than likely calcium.
    4. If no flakes remain, it could be White Water Mold or biofilm.

    Depending on the outcome of this test will determine what you should do next. If it is White Water Mold, then please read this post on how to remove the mold https://hot-tub-blog.spadepot.com/2018/03/16/mold-and-mildew-in-a-hot-tub/.

    If it is excess calcium, try using a hose end fill filter (https://www.spadepot.com/Pre-Fresh-Spa-Pool-Water-Fill-Filter-P2666) after flushing and draining your spa. Then use a product such as Spa Defense (https://www.spadepot.com/Spa-Defense-Scale-Preventer-32oz-P2040) to prevent excessive calcium in the future.

    Please let us know if you have any other questions!

    Thank you,


  14. We need help getting the sanitizer level correct. It is low (15)
    We use nature,s choice spa mineral purifier and xtra blue shock.


  15. I have the spa frog inline system and ozone generator, I have stopped using bromine and am now using the Frog silver clonine cartridge. Should I or can I still use the blue mineral cartridge?


  16. Hi Jan,

    When using a mineral sanitizer, there is no need to keep your chlorine level at the standard range. Shocking about once a week is good. If you use your spa daily or don’t shower before use, you may need to up that to 2 times per week.



  17. Hi Larry,

    If I understand you correctly, you are switching from the standard Spa Frog system to the @ease cartridges. You will want to use both the silver chlorine cartridge and the blue mineral cartridge, and do not use any other cartridges from the old system.



  18. Are you able to tell me the difference between Theralux Spa Sanitiser and Spa Shock Sanitiser and do they both work in a hot Spa.


  19. Hi Merle,
    The Australia only Theralux appears to be a mixture of Borax, MPS, and clarifier. The Borax is used to control algae, which means it’s geared towards pool use rather than spa use. Many products can be used as a Spa Shock Sanitizer, so it’s hard to compare a product without knowing specifically which one you’re interested in. We do carry hot tub specific product that’s an all in one conditioner, water balancer, shock and clarifier, found here: https://www.spadepot.com/EZ-Spa-Total-Care-2-lb-P836.



Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s