Concerns About Ahh-some Products, BACs, and Antibiotic Resistance in Hot Tub Maintenance

[eco-help]

Hello everyone,

I've been using Ahh-some products (gel and Aqua Clarity) to purge and maintain my prior hot tubs. Recently, I was diagnosed with infections caused by Pseudomonas and Mycobacterium Abscessus (MAC), and I've been undergoing treatment with multiple antibiotics.

I've come across comments and references suggesting that BACs (benzalkonium chlorides), commonly used in spa maintenance products, might contribute to bacteria developing resistance to antibiotics. As someone who relies on a limited number of antibiotics that are effective against my infections, this is a significant concern for me.

Here's the specific comment and research information that concerns me: Link to forum post.

I have a couple of questions:

1. Has anyone come across recent research or reliable sources discussing the interaction between BACs and the resistance of bacteria like Pseudomonas and MAC to antibiotics?
2. Are there alternative hot tub maintenance products or methods that might be safer for individuals dealing with antibiotic-resistant bacteria?
3. Any personal experiences with maintaining a hot tub while managing similar health conditions would be greatly appreciated.

Thank you for your help and information.

 

[PoolStored]

Maybe @Ahhsomeguy can weigh in...

 

[Ahhsomeguy]

It looks like your initial post regarding our Ahhsome/AquaClarity products was 10 years ago.
Have you been using the products since then?
What sanitizer are you using on a regular basis?
Have you performed periodic purges and full drain downs? I believe I remember speaking with you way back. I see you are from Tampa.

 

[VinnyinNJ]

I'm not a scientist but this is what I know. Basically there are at least 4 known disinfectants - ozone, chlorine, bromine and peroxide, there may be more that I'm not aware of. Ozone is the most powerful disinfectant followed by chlorine. They are whats used in drinking water. Hot tubs do have issues with bacteria, at the tubs temp (100+ F) bacteria doubles about every 20 minutes. Biofilm can develop in a tub if left unprotected with a disinfectant. In years past ozone in a tub was a joke, it may not be today. So that leaves chemical disinfectants. I used chlorine in my tub and the rule of thumb in the past was to have 3 PPM chlorine in the tub 20 minutes after dosing the tub. Back then it was also recommended to shock the tub to about 15 PPM once a week to kill whatever was in the water. 20 years ago, I was on a forum that had a microbiologist as a member and he tested his water all the time and it was OK. Again, back then we used strictly dichlor which builds up stabilizer which makes chlorine less effective but bacteria is more fragile so it works, just takes a bit longer.

Then Ahhsome came around, I only used their purge product and it changed the way people cleaned their tub. At the time we would add a lot of bleach - up to 25 or more PPM as we purged the tub; it was cleaned and disinfected. Another thing that happened is that this forum had a person, ChemGeek, who found the forum that I was on (I knew him from here) and spoke about using dichlor up until you hit 30 PPM stabilizer then use bleach. Another game changer! The problem comes when people don't stick to a good regiment of disinfection. So keeping the tub at 3 PPM chlorine ( the other disinfectants have different numbers), don't miss days of no disinfectant, shock once a week just in case, purge the tub with Ahhsome on water changes (I would add additional chlorine as well) and don't miss water changes. Since I had the opportunity to "hang out" on a forum with a microbiologist I feel confident that the above is a safe way to use a tub. Maybe someone with more knowledge will come along and give better info.

 

[phonedave]

Hello everyone,

I've been using Ahh-some products (gel and Aqua Clarity) to purge and maintain my prior hot tubs. Recently, I was diagnosed with infections caused by Pseudomonas and Mycobacterium Abscessus (MAC), and I've been undergoing treatment with multiple antibiotics.

I've come across comments and references suggesting that BACs (benzalkonium chlorides), commonly used in spa maintenance products, might contribute to bacteria developing resistance to antibiotics. As someone who relies on a limited number of antibiotics that are effective against my infections, this is a significant concern for me.

Here's the specific comment and research information that concerns me: Link to forum post.

I have a couple of questions:

1. Has anyone come across recent research or reliable sources discussing the interaction between BACs and the resistance of bacteria like Pseudomonas and MAC to antibiotics?
2. Are there alternative hot tub maintenance products or methods that might be safer for individuals dealing with antibiotic-resistant bacteria?
3. Any personal experiences with maintaining a hot tub while managing similar health conditions would be greatly appreciated.

Thank you for your help and information.

I am far from being a qualified Biological Chemist, so take all of my responses here with a grain of salt. However my wife also relies on a limited number of antibiotics (she is highly allergic to most antibiotics, and almost all of the modern ones) so antibiotic resistance is something that we keep in mind, but again are by no means experts.

However, from what I have seen, it is not so much that BAC can cause antibiotic resistance in bacteria, but that there is a cross linkage between SANTIZIERS IN GENERAL and antibiotic resistance.

I guess the answer is, if you are trying to kill bacteria, then make sure you kill it all. Don't use a low level of sanitizer that leaves some hanging around with a chance to mutate into something stronger. Kill it dead the first time.

 

[eco-help]

It looks like your initial post regarding our Ahhsome/AquaClarity products was 10 years ago.
Have you been using the products since then?
What sanitizer are you using on a regular basis?
Have you performed periodic purges and full drain downs? I believe I remember speaking with you way back. I see you are from Tampa.

Hi Ahhsomeguy,

Thank you for your response and for your attention to my past usage of Ahh-some products. While I appreciate the importance of proper maintenance practices, my main concern revolves around the potential link between benzalkonium chlorides (BACs) and antibiotic resistance.

I've encountered some references and comments suggesting that BACs, used in spa maintenance products like Ahh-some, might contribute to bacteria developing resistance to antibiotics. This is particularly worrying for me as my health condition limits my options to a narrow range of effective antibiotics.

Understanding that your formulation is proprietary, could you provide any (general) insights or assurances regarding the safety of Ahh-some products in relation to BACs and their potential impact on antibiotic resistance? Is there a way to use the product to ensure that the BACs do not have the ability to impact antibiotic resistance? Additionally, are there any alternative products or practices you would recommend for someone with my health considerations?

Regarding your questions, I've made my best efforts in maintaining proper sanitation, though there have likely been lapses since owning the Bullfrog spas (I had 3, 2 were warranty replacements) for about 3 years. I follow the Dichlor/bleach method as recommended on this forum. In the first two Bullfrog spas, I periodically used the Ahh-some gel to purge and AquaClarity for weekly maintenance, but I used it less often due to concerns about BACs and the detergent feel. For my new hot tub, which I just purged, I didn't have the gel, so I used AquaClarity (12 oz for a 400-gallon hot tub). I have not used the AquaClarity product for weekly maintenance. Unless I find a better approach, my plan is to continue following the Dichlor/bleach method, shocking with bleach weekly or after heavy bather loads, and emptying/refilling every 2-3 months, while planning to purge on either a 6 or 12-month schedule.

I appreciate your understanding and look forward to your guidance on this matter.

Thank you.

 

[Ahhsomeguy]

Good Morning Eco-help: I appreciate you answering my recent questions as to your hot tub maintenance protocols. Let be first begin by stating that I cannot advise you on any of your health related issues. Your physicians should be consulted and give you specific information as to the use of chemicals in your hot tub.
I can tell you this. BAC was first discovered in 1935 and have been widely used worldwide. Resistance to antibiotics is and has been a nagging issue for many years with the growing use of many products and medicinal antibiotics. Here is what I can tell you regarding the use of Ahh-Some Gel or Aqua Clarity in your hot tub.
Our Ahh-Some Gel product is used to "Purge" contaminants and biofilms from surfaces. It is the superior product for the job. Within minutes we breach the cellular walls of slim-forming biofilm matrixes and fully expose them so your chlorine or bromine can eradicate them. After purging you drain your tub. The residual Ahh-Some after refilling is zero or extremely low based on how well you rinse and wipe the shell.
AquaClarity is a diluted version of the gel. AquaClarity is further diluted when mixed with the 122 ounces of water to make the gallon. As you have done yourself, you can purge the hot tub with the AC by using 3 ounces of mixed product for every 100 gallons of water in your tub. It works great and essentially does the same work as the gel for the purge. In addition to using the AC to purge biofilms it can be used as a weekly maintenance product by adding 1 ounce of AC for each 200-250 gallons of water every week. So, the AC is heavily diluted at the start and then you are adding a very small amount to 400 gallons of water that further dilutes the already diluted liquid. My point is this. The amount of BAC in your hot tub for the weekly maintenance dose is extremely low. It is very unlikely that the amount of product you would be soaking in would contribute to your health issues.
However, based on your provided information regarding your health issues it would seem most prudent on your part to only use our product(s) for purging your hot tub. I do recommend the di-chlor bleach method for sanitization. I have been using that method along with our AquaClarity for well over 12 years now and have never had clarity or biofilm issues. I wish you good health my friend. Thank you for your support over the years. It is appreciated.

 

[phonedave]

Good Morning Eco-help: I appreciate you answering my recent questions as to your hot tub maintenance protocols. Let be first begin by stating that I cannot advise you on any of your health related issues. Your physicians should be consulted and give you specific information as to the use of chemicals in your hot tub.
I can tell you this. BAC was first discovered in 1935 and have been widely used worldwide. Resistance to antibiotics is and has been a nagging issue for many years with the growing use of many products and medicinal antibiotics. Here is what I can tell you regarding the use of Ahh-Some Gel or Aqua Clarity in your hot tub.
Our Ahh-Some Gel product is used to "Purge" contaminants and biofilms from surfaces. It is the superior product for the job. Within minutes we breach the cellular walls of slim-forming biofilm matrixes and fully expose them so your chlorine or bromine can eradicate them. After purging you drain your tub. The residual Ahh-Some after refilling is zero or extremely low based on how well you rinse and wipe the shell.
AquaClarity is a diluted version of the gel. AquaClarity is further diluted when mixed with the 122 ounces of water to make the gallon. As you have done yourself, you can purge the hot tub with the AC by using 3 ounces of mixed product for every 100 gallons of water in your tub. It works great and essentially does the same work as the gel for the purge. In addition to using the AC to purge biofilms it can be used as a weekly maintenance product by adding 1 ounce of AC for each 200-250 gallons of water every week. So, the AC is heavily diluted at the start and then you are adding a very small amount to 400 gallons of water that further dilutes the already diluted liquid. My point is this. The amount of BAC in your hot tub for the weekly maintenance dose is extremely low. It is very unlikely that the amount of product you would be soaking in would contribute to your health issues.
However, based on your provided information regarding your health issues it would seem most prudent on your part to only use our product(s) for purging your hot tub. I do recommend the di-chlor bleach method for sanitization. I have been using that method along with our AquaClarity for well over 12 years now and have never had clarity or biofilm issues. I wish you good health my friend. Thank you for your support over the years. It is appreciated.

As a data point of one, we have been using AquaClarity and DiChlor/Bleach in our hot tub for a while now (over a year) with no adverse impacts (no bacterial infections).

As I said above, my wife is allergic to most antibiotics. My wife is also VERY immune compromised. For a fun read, look up the genetic condition CVID. Common Variable Immune Deficiency. - Common variable immunodeficiency - Wikipedia

She has had no issues with our hot tub sanitation routine.

Again, a data point of one, but it is what it is.

 

[eco-help]

I am far from being a qualified Biological Chemist, so take all of my responses here with a grain of salt. However my wife also relies on a limited number of antibiotics (she is highly allergic to most antibiotics, and almost all of the modern ones) so antibiotic resistance is something that we keep in mind, but again are by no means experts.

However, from what I have seen, it is not so much that BAC can cause antibiotic resistance in bacteria, but that there is a cross linkage between SANTIZIERS IN GENERAL and antibiotic resistance.

I guess the answer is, if you are trying to kill bacteria, then make sure you kill it all. Don't use a low level of sanitizer that leaves some hanging around with a chance to mutate into something stronger. Kill it dead the first time.

thanks for your reply! Noted on sanitzer, I am doing my best, but without SWG it's hard to keep up. (think travel, hurricanes, torrential rain, sickness etc). Might have to consider Bromine but that just seems like more stuff & $ and still have to add chlorine weekly.

 

[eco-help]

As a data point of one, we have been using AquaClarity and DiChlor/Bleach in our hot tub for a while now (over a year) with no adverse impacts (no bacterial infections).

As I said above, my wife is allergic to most antibiotics. My wife is also VERY immune compromised. For a fun read, look up the genetic condition CVID. Common Variable Immune Deficiency. - Common variable immunodeficiency - Wikipedia

She has had no issues with our hot tub sanitation routine.

Again, a data point of one, but it is what it is.

Sorry to hear about your wife I have a tiny idea what she must be going through...
Good to know your finding the dichlor/bleach method and aquaclarity works.. are you doing ahhsome purge (gel?) then weekly aquaclarity? How often do you change the water/purge?

 

[eco-help]

Good Morning Eco-help: I appreciate you answering my recent questions as to your hot tub maintenance protocols. Let be first begin by stating that I cannot advise you on any of your health related issues. Your physicians should be consulted and give you specific information as to the use of chemicals in your hot tub.
I can tell you this. BAC was first discovered in 1935 and have been widely used worldwide. Resistance to antibiotics is and has been a nagging issue for many years with the growing use of many products and medicinal antibiotics. Here is what I can tell you regarding the use of Ahh-Some Gel or Aqua Clarity in your hot tub.
Our Ahh-Some Gel product is used to "Purge" contaminants and biofilms from surfaces. It is the superior product for the job. Within minutes we breach the cellular walls of slim-forming biofilm matrixes and fully expose them so your chlorine or bromine can eradicate them. After purging you drain your tub. The residual Ahh-Some after refilling is zero or extremely low based on how well you rinse and wipe the shell.
AquaClarity is a diluted version of the gel. AquaClarity is further diluted when mixed with the 122 ounces of water to make the gallon. As you have done yourself, you can purge the hot tub with the AC by using 3 ounces of mixed product for every 100 gallons of water in your tub. It works great and essentially does the same work as the gel for the purge. In addition to using the AC to purge biofilms it can be used as a weekly maintenance product by adding 1 ounce of AC for each 200-250 gallons of water every week. So, the AC is heavily diluted at the start and then you are adding a very small amount to 400 gallons of water that further dilutes the already diluted liquid. My point is this. The amount of BAC in your hot tub for the weekly maintenance dose is extremely low. It is very unlikely that the amount of product you would be soaking in would contribute to your health issues.
However, based on your provided information regarding your health issues it would seem most prudent on your part to only use our product(s) for purging your hot tub. I do recommend the di-chlor bleach method for sanitization. I have been using that method along with our AquaClarity for well over 12 years now and have never had clarity or biofilm issues. I wish you good health my friend. Thank you for your support over the years. It is appreciated.

Thank you for your reply. I appreciate and understand many of the points you've made, and I plan to consult with my specialist on my next visit this week.

That being said, it seems there may have been a misunderstanding or oversight regarding my primary concern. I'm not questioning the safety of your product in terms of skin interaction. Instead, my main concern centers on the potential connection between benzalkonium chlorides (BACs) and antibiotic resistance, as detailed in the article I previously linked.

Has your company conducted or reviewed research that confirms your product does not contribute to antibiotic resistance? Such information would be a significant advantage for your product compared to others that also use BACs.

While you note that BACs have been in use for a long time, it's important to acknowledge that numerous products with long-standing use have been found to cause cancer or other adverse effects. Unfortunately, many of these products remain available in the U.S., even though some have been banned in other countries.

 

[eco-help]

I'm not a scientist but this is what I know. Basically there are at least 4 known disinfectants - ozone, chlorine, bromine and peroxide, there may be more that I'm not aware of. Ozone is the most powerful disinfectant followed by chlorine. They are whats used in drinking water. Hot tubs do have issues with bacteria, at the tubs temp (100+ F) bacteria doubles about every 20 minutes. Biofilm can develop in a tub if left unprotected with a disinfectant. In years past ozone in a tub was a joke, it may not be today. So that leaves chemical disinfectants. I used chlorine in my tub and the rule of thumb in the past was to have 3 PPM chlorine in the tub 20 minutes after dosing the tub. Back then it was also recommended to shock the tub to about 15 PPM once a week to kill whatever was in the water. 20 years ago, I was on a forum that had a microbiologist as a member and he tested his water all the time and it was OK. Again, back then we used strictly dichlor which builds up stabilizer which makes chlorine less effective but bacteria is more fragile so it works, just takes a bit longer.

Then Ahhsome came around, I only used their purge product and it changed the way people cleaned their tub. At the time we would add a lot of bleach - up to 25 or more PPM as we purged the tub; it was cleaned and disinfected. Another thing that happened is that this forum had a person, ChemGeek, who found the forum that I was on (I knew him from here) and spoke about using dichlor up until you hit 30 PPM stabilizer then use bleach. Another game changer! The problem comes when people don't stick to a good regiment of disinfection. So keeping the tub at 3 PPM chlorine ( the other disinfectants have different numbers), don't miss days of no disinfectant, shock once a week just in case, purge the tub with Ahhsome on water changes (I would add additional chlorine as well) and don't miss water changes. Since I had the opportunity to "hang out" on a forum with a microbiologist I feel confident that the above is a safe way to use a tub. Maybe someone with more knowledge will come along and give better info.

Hi VinnyinNJ, (sorry for my late reply)

Thank you for sharing such a detailed and insightful explanation of the different disinfectants used in hot tubs and the importance of maintaining a rigorous disinfection routine. Your experience and practical advice offer a valuable perspective, especially regarding the use of Ahh-some and maintaining proper chlorine levels.

While my main concern is about the potential link between benzalkonium chlorides (BACs) and antibiotic resistance, your insights into general disinfection practices will certainly help me manage my hot tub more effectively.

I appreciate your input and the time you took to elaborate on these points. It's been very helpful!

 

[VinnyinNJ]

Hi VinnyinNJ, (sorry for my late reply)

Thank you for sharing such a detailed and insightful explanation of the different disinfectants used in hot tubs and the importance of maintaining a rigorous disinfection routine. Your experience and practical advice offer a valuable perspective, especially regarding the use of Ahh-some and maintaining proper chlorine levels.

While my main concern is about the potential link between benzalkonium chlorides (BACs) and antibiotic resistance, your insights into general disinfection practices will certainly help me manage my hot tub more effectively.

I appreciate your input and the time you took to elaborate on these points. It's been very helpful!

The hot tub forum I was on the main sanitizer used was chlorine. There was some people who used bromine but had issues and there was one person who used hydrogen peroxide. Bromine users spoke about how hard it was to keep the sanitizer levels in the tub up. The one person who used peroxide I think used 35% peroxide, it was not a recognized hot tub sanitizer back then. There was Baqua Spa but it had/has big issues and I wouldn't recommend it at all which is why I didn't list it originally.

I can't speak about your main concern but over the years that I had the tub running I made sure to follow a disinfection routine. Mine was slightly different then posted above based on the microbiologist's recommendations but it would be inappropriate for your use. People back then and maybe still do rely on ozone to kill the nasties but the ozone systems back then were not great at producing the amount of ozone or contact area needed to effectively kill bacteria. If I had a party and people were going to use the tub I would put a dose in before they used it, once they got out to eat or take a break from it and then once the party was over. I would keep vials of bleach so it wasn't a big deal to pop them in. The problem lies when people skip days of dosing because of whatever reason. Theoretically, if you dosed to get 3 PPM chlorine 20 minutes later then if the next morning you have 1 PPM left the chlorine is still doing it's job. But that's not a safe level for someone who might be susceptible to infections.

Also, the skin can be a barrier to bacteria assuming no cuts/openings to make bacteria enter. In all the years of using my tub I had only one person claim they got "Hot Tub Rash" from it but there were other people using the tub at the same time with no symptoms. I can't say it was or wasn't, I suspect it wasn't.

I'm just a hot tub user so please take what I posted with a grain of salt if better information is out there!

 

[JoyfulNoise]

Quaternary ammonium compounds (QACs) have rarely been shown to cause antibiotic resistance in real world settings. There’s certainly lots of lab studies that show how a bacteria or virus can develop resistance to the biocidal activity of QAC’s but what happens in a Petri dish rarely reflects reality in everyday use. This study provides a good meta analysis of QAC resistance -

Quaternary ammonium disinfectants and antiseptics: tolerance, resistance and potential impact on antibiotic resistance - PMC

Due to the substantial increase in the use of disinfectants containing quaternary ammonion compounds (QACs) in healthcare and community settings during the COVID-19 pandemic, there is increased concern that heavy use might cause bacteria to develop ...

pmc.ncbi.nlm.nih.gov

It should be noted that the above article states that Psuedomonas is known to have higher levels of resistance to QAC compounds than other bacteria due to innate properties of the bacteria’s structure and biochemistry.

One general comment to highlight from this thread is that Ahhsome is NOT intended to be a hot tub sanitizer. Its use in hot tubs is mainly for its ability to breakdown biofilms created by bacterial colonies as well as act as a surfactant that lifts films off plumbing surfaces. It also acts as a bulk water clarifier to help the filter capture particulates. The sanitizing chemical in any hot tub should be either bromine or chlorine and it should be kept at a level that is sufficient to produce an appropriate kill rate. Chlorine is a very effective, broad spectrum and fast sanitizer that kills a wide variety of bacteria, viruses, and molds/algae/fungi. When used properly, it is effective and safe and has almost never been shown to induce biological resistance. Everything else used in a hot tub should be merely considered an adjunct chemical to improve water quality.

 

[wireform]

But I think Ahhsome is also tell tale of how well sanitized the tub was managed just by what it does or doesn't bring up when a purge is being done.

 

[JoyfulNoise]

But I think Ahhdome is also tell tale of how well sanitized the tub was managed just by what it does or doesn't bring up when a purge is being done.

Agreed. Improperly or infrequently sanitized hot tubs can generate bacterial infestations very quickly. Hot tubs operate in what is colloquially known as “The Goldilocks Zone” of biology - not too hot, not too cold, but juuuuust right for growth. The temperature is perfect for rapid cell division and hot tubs offer plenty of organic compounds and nutrients for bacteria to use as an energy source. The human body has more bacteria in its gut alone than the entire cell count of a human. Our skin and hair are literally covered in bacterial colonies. So when a person gets into a tub, that bacterial load is shed directly into the water along with sweat, urine, feces and dead skin and hair cells. Phosphates, nitrates and potassium build up in the water body and are not removed. Given those conditions, the water will figuratively explode with bacterial growth once the sanitizer concentration falls below the kill rate necessary to overcome the growth rate.

We don’t call it “human soup” around here for no reason

 

[phonedave]

Sorry to hear about your wife I have a tiny idea what she must be going through...
Good to know your finding the dichlor/bleach method and aquaclarity works.. are you doing ahhsome purge (gel?) then weekly aquaclarity? How often do you change the water/purge?

I purge with AhhSome when I do a water change. However, after using AquaClarity for over a year now, it has become unnecessary. I get nothing in the foam when I purge anymore (but I still use it - I also use it in my jetted tub and my washing machine so I have it on hand.

I change my hot tub water every 3 to 5 months. It depends on how the winter goes. I last changed my hot tub in late November, and looking at the weather and my schedule, likely will not again until early April. The good news is that we also do not use the tub as much in the winter. In the nice weather, when we use the tub more, I tend to change it more frequently. Doing a water change is only a couple of hours. The tub is out of commission for a while until it gets back to temp, but the actual time spent working on it is not that long.

Here is something else that I have found with AC. The AC cleans it so well that I can get away without adding bleach for quite some time (4-5 days). Now, I do have ozone in the tub as well, so that may be a factor. But I can let the tub go for a number of days, while nobody is using it, and then check it. The FC will be low, as in 0.5, but there will be no CC's at all. When that happens I run it up the SLAM levels and check the next day, and everything is back to normal. Going on vacation is not really a concern. It just takes 24 hours or so once we get back to confirm that nothing has started to grow in there.

 

[VinnyinNJ]

As far as changing hot tub water, if you can schedule the water change around Thanksgiving that will bring you to around this time of year for the next water change. Purging and draining isn't too bad when it's around 40F or higher. Using a sump pump makes draining go really fast and the tub is up to temp by next morning assuming you have a 220V tub.

 

[JoyfulNoise]

I have always advocated for doing frequent water exchanges, as many as you can reasonable do and at a reasonable cost. Just from a chemical/biological standpoint, the bather load in tubs is just so high that the water builds up a substantial dissolved organic and inorganic content very quickly.

There's a test that can be done on water, and it's often done at water treatment facilities, called chemical-oxygen demand (COD). It's a measure of all the dissolved junk in the water that can be possibly oxidized from its current form to some other form. Both organic compounds and some inorganic compounds contribute to the COD. A high COD typically indicates that the water has a lot of dissolved organics in it and that it is not potable. Reduction in COD is one of the first processes called for in water treatment. Sadly, the COD test requires a laboratory environment to do it right as it takes time and heat to perform the test and uses reagents that are not easily worked with (and can be dangerous). But my hunch is that if you took hot tub water and measured the COD at regular intervals, you'd see it go way up right after initial use and then remain very high. While chlorine is a good oxidizer, it is not capable of oxidizing everything to completion and/or it can be very slow at it. So while chlorine will keep a tub sanitary, it doesn't reduce COD as much and that high COD is what will drive biological outbreaks. So the only realistic solution to reducing COD (as well as dissolved and suspended solids) is to exchange used water for fresh water.