biofilms - why 1-3ppm FC is not enough

dlleno

Well-known member
Sep 9, 2016
100
denver, CO
Greetings Hot Tub enthusiasts

Those who are familiar with my work know that I have spent large amounts of time and water, testing various purge products. This post is not about that - it is instead dedicated to the little-known fact that biofilms can apparently survive and even grow in the presence of chlorine.

Did you know that that?

One of the references cited in my original work (see below) describes a controlled experiment with the simulated bather load, water filtration and turn-over rate of a swimming pool. Their laboratory model was "challenged with a bacterial load and synthetic bather insult, formulated to represent urine and perspiration". The purpose of this work was to study the effectiveness of two common sanitizers, chlorine and biguanide. In a rather stunning statement in their abstract, the researchers describe that "biofilm was able to accumulate on coupons and in the filter systems of reactors treated with either 1–3 mg/L free chlorine or 10 mg/L polyhexamethylene biguanide (PHMB) (emphasis mine). The abstract goes on to describe that the biofilm accumulations were considerably attenuated compared to the control, but the astonishing thing is that they accumulated at all -- in the presence of 1-3ppm FC and in the normal bather load of a swimming pool.

This connects a lot of dots, and demonstrates that the high bather load, higher water temperatures, and more widely fluctuating sanitizer levels of a Hot Tub present an even more hospitable petri dish for bad guys. We should be even more careful than the pool side of the house, not only with regular shock treatments but with regular purges designed to break up and release biofilms. I used to be an advocate of letting your purge results dictate how often you purge, but now I am an advocate of purging upon every drain. full stop. its so easy to dose with ahh-some right before you drain, and the work you go through, wiping everything all those surfaces, will remind you of the importance of your work.

Also -- let this portion of the paper's abstract keep ringing in your ears: biofilm accumulates in the filter, even with chlorine present! (emphasis mine). This is why it is so important to "purge" your filters too, at the same time as you purge your tub. I cut a piece of PVC pipe just the right length to hold all of my filters, to keep them from clogging up the skimmer weir.

"death to biofilms..."





Controling biofilms in spas and hot tubs - PART 1

Evaluation of disinfectant efficacy against biofilm and suspended bacteria in a laboratory swimming pool model by D.M Goeres, T Palys, B.B Sandel, and J Geiger
 

JJ_Tex

Bronze Supporter
Jul 17, 2019
965
Prosper, TX (DFW)
Isnt TFP all about the relationship between CYA and Chlorine? I dont see CYA levels mentioned at all in the write-up, but even at a low CYA of 30, the recommended FC levels here are 4-6, so not shocking you found bad stuff growing at FC of 1-3.

Apologies if I am off base or missing something, as I do not have a stand alone spa, only a pool/spa combo.
 
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carnivalday

Gold Supporter
Bronze Supporter
Oct 25, 2017
413
Ocala, FL
Im a little confused why the experiment used a FC level so low, when recommended levels in pools are nearly twice what the experiment was.
 

dlleno

Well-known member
Sep 9, 2016
100
denver, CO
This study was meant to study the effectiveness of 1-3ppm FC in a swimming pool, and there is no mention of CYA (that I found), so you'll have to draw your own conclusions on that. It was a laboratory simulation. I posted for the benefit of those who accumulate the weight of evidence that's all. the growing biofilms were attenuated to a 4 log reduction too, compared to the control., so perhaps there are some who will read this and conclude that they don't have to shock. Just please realize that no one has a definitive study characterizing how biofilms grow in all situations, so you have to read these kinds of studies with the purpose for which they are intended.

If I could guarantee that my hot tub always exceeded every condition described by this study, including its bather load, filtration and water turnover then I'd be inclined to question its relevance too. you might also check out the post title -- its revealing. Moreover, if there is a study showing that the extra 2ppm removes all doubt and exonerates all hot tubs in all situations from all risks of accumulating biofilms, then I want to see that one, to be sure.
 
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JJ_Tex

Bronze Supporter
Jul 17, 2019
965
Prosper, TX (DFW)
So you are recommending regular shocking to prevent biofilm? Is that a stand alone spa thing? Sorry for the questions, but it seems contrary to the basic TFP principles of maintaining your FC/CYA levels and your pools will be trouble free.
 

dlleno

Well-known member
Sep 9, 2016
100
denver, CO
Well my basic tenant is that those of us who are proud of our water maintenance skills are still vulerable to biofilm growth and that we might not be as immune as we think. The evidence is growing that the particular conditions specific to portable spas (associated with very high bather load) and moments of less than 3ppm fc, combined with a robust food supply in the form of oils and other materials not fully oxidized, puts the tub at risk . Purges with ahh-some are not just a rescue step they should be a regular event if only to reduce the biofilm food supply. Im an advocate of the maintenance we revere here combined with regular purges, as opposed to regular shocks. But im not dissing shocks by any means.

On a personal note im not a fan of shocking although have done a SLAM as a rescue for bad behavior lol (id rather maintain the water correctly and purge on every drain) but there's benefit especially if you don't purge regularly. I didnt mean to suggest that regular shocking was the answer (that was the study conclusion not mine) but at the same time i just dont think its wise to think that the maintenance skills of which we are so proud will result in zero biofilms 100% of the time , for ever and ever, not even in the filters. Ahhsome is much more effective at controlling biofilms than attenuating them with a traditional decon
 
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JJ_Tex

Bronze Supporter
Jul 17, 2019
965
Prosper, TX (DFW)
Got it, and thanks for the detail. In my simpleton brain I'm hearing: Stand alone spas have a smaller margin of error than a typical pool because they are smaller bodies of water and at times can have a very high concentration of people in that body of water. As such, purging and shocking (less preferred) should be incorporated into proper spa water management.
 

dlleno

Well-known member
Sep 9, 2016
100
denver, CO
That's a good summary! I would only add to my own epistle that impecable water maintenance in a portable spa may reduce the need for shocking but not the need for purging
 
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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
16,589
Tucson, AZ
Studies have been done (I’d have to go searching for the references again) that have exposed biofilms to unstabilized FC concentrations above 200ppm and the biofilms remain intact. Not only that, but the diffusion of chlorine is so low that only the first few micrometers (millionth of a meter) are affected by the chlorine but the bulk of the film is unexposed. Bacteria build up thick biofilm layers and reside throughout the film thickness. So chlorine, at best, kills just the bacteria near the surface of the film but leaves the reservoir of bacteria intact and viable.
 
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Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
4,757
Central California
Is this something a pool owner with no spa has to consider, one who targets his FC around 5-6, but has been known to let it slip on occasion this time of year to 2 or 3 (darn water is too cold for SWG), or can I go back to watching my old Star Trek episodes on Netflix?
 
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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
16,589
Tucson, AZ
Is this something a pool owner with no spa has to consider, one who targets his FC around 5-6, but has been known to let it slip on occasion this time of year to 2 or 3 (darn water is too cold for SWG), or can I go back to watching my old Star Trek episodes on Netflix?
Biofilms are less likely to form in pool plumbing as bacterial growth tends to be less of an issue (algae is the bigger issue). Hot tubs are very susceptible to bacterial growth because they are typically kept covered, they are usually held at the “Goldilocks temperature”, and the sanitizer levels fluctuate a lot more frequently.

Your FC levels are fine. Your winter pool water temps are too low for anything to grow. Gonna into your binge watching.
 
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dlleno

Well-known member
Sep 9, 2016
100
denver, CO
0
Studies have been done (I’d have to go searching for the references again) that have exposed biofilms to unstabilized FC concentrations above 200ppm and the biofilms remain intact. Not only that, but the diffusion of chlorine is so low that only the first few micrometers (millionth of a meter) are affected by the chlorine but the bulk of the film is unexposed. Bacteria build up thick biofilm layers and reside throughout the film thickness. So chlorine, at best, kills just the bacteria near the surface of the film but leaves the reservoir of bacteria intact and viable.
Got any references/ citations? This is precisely why a purge that breaks up and releases biofilms is most effective, and confirms why a traditional decon is relatively impotent in the fight against biofilms
 

Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
4,757
Central California
Just curious (more for other pool owners, 'cause I don't do these things): if I kept my pool really warm (in the 90s, 24/7) and kept it covered to achieve that, would my pool be more susceptible to biofilm (I'm thinking FL or TX)? Or is temps in the low 100s needed? If my pool did succumb to biofilm, would it all die off in the winter (water temps in the 40s), or would these described "bio layers" protect the bacteria until next swim season?
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
16,589
Tucson, AZ
0


Got any references/ citations? This is precisely why a purge that breaks up and releases biofilms is most effective, and confirms why a traditional decon is relatively impotent in the fight against biofilms

I can't post the reprint I have as it would violate copyright laws but here is the citation if you can find it on your own and an excerpt from the conclusions -

Direct Measurement of Chlorine Penetration into Biofilmsduring Disinfection
DIRK DE BEER, ROHINI SRINIVASAN, AND PHILIP S. STEWART

APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Dec. 1994, Vol. 60, No. 12, p. 4339-4344

Comparison of the cross sections and chlorine microprofiles
leads to the conclusion that decreased action of chlorine
against biofilms is due to limited penetration stemming from a
reaction-diffusion interaction. The microprofiles show that,
after exposure to 2.5 ppm of chlorine for 1 h, only the upper
100µm of the cell clusters is penetrated by chlorine. This
correlates reasonably well with the microscopic images show-
ing that the top half of the cell clusters have lost their
respiratory activity. Exposure to very high chlorine concentra-
tions leads to complete penetration of biocide and also stops
the respiratory activity in the whole biofilm.
My bad memory about the high concentration profiles. Their "very high chlorine" concentrations are roughly 6 times higher than the standard concentration they use (2.5ppm). But on the high concentration end, it still required as long as 30mins of exposure time to get complete penetration of the chlorine and, in almost all of their coupons tested, there was no noticeable lifting of the biofilm. The higher concentrations simply bleach out the biofilm.

Considering the experiments are done using unstabilized chlorine, a concentration of 16ppm FC with no CYA is roughly 8ppm hypochloroous acid (HOCl). That high of a concentration of HOCl would be extremely irritating to anyone standing near the tub and damaging to hot tub equipment. So it goes to show that it is unrealistic to expect chlorine to remove or compromise biofilms in anyway. Your experiments in this area confirm that only a purge that lifts biofilms away so they can be mechanically removed by filtration and draining will be effective at cleaning out a hot tub.
 
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As per Jerry at Ahhsome / Hot Tub Serum:

"The way it works is that it breaks through the lipid layer of the biofilm so that the chlorine can then kill or oxidize it. Sanitizer by itself such as chlorine and bromine cannot penetrate this lipid layer."


 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
16,589
Tucson, AZ
Just curious (more for other pool owners, 'cause I don't do these things): if I kept my pool really warm (in the 90s, 24/7) and kept it covered to achieve that, would my pool be more susceptible to biofilm (I'm thinking FL or TX)? Or is temps in the low 100s needed? If my pool did succumb to biofilm, would it all die off in the winter (water temps in the 40s), or would these described "bio layers" protect the bacteria until next swim season?
You could cause bacterial growth in a pool but sunlight really limits the activity of bacterial. Bacteria, in general, prefer environments where light is excluded. So you could get biofilm formations in your plumbing. This is the chief problem with Baquacil pools - the sanitizer is often not kept at effective levels and that allows biofilms and bacterial growth as well as mold and fungi. Once that happens, there’s no easy way to destroy those pathogens because adding chlorine to a Baquacil pool creates a huge mess. So then Baquacil users have to resort to all sorts of extreme measures to get the pool back to a clear and sanitary state.

Cold weather would not kill bacteria or degrade biofilms, they simply go dormant and then start multiplying again when the water warms up.
 

Backcountryski

Well-known member
Aug 31, 2019
46
WA
I just did a purge with Ahh-some yesterday. First time for me as this is a new tub. Yes, I know I should have purged it prior to use, but I did not have the ahh-some yet, and I wanted to use my tub, so I just went for it. Yesterday's results were a fair amount of lime green sludge that was released. I am a believer and I will purge everytime I change the water, for the low cost of the ahh-some, there really is no reason not to.

On a side note, I did not float my filters in the tub. I was expecting quite a bit of sludge to come out and I was worried about it getting into the filters. After seeing how sticky that stuff was, I think I made the right choice. I clean my filters monthly and they are only 4 months old. Next time I will probably soak them in the ahh-some...
 

dlleno

Well-known member
Sep 9, 2016
100
denver, CO
Yea you did the right thing. You can also save some ahhsome dosed water in a bucket for the filters. In fact i do that anyway for wiping stuff down.

In one of my experiments i showed that biofilms accumulate in the filter media by cleaning them first with a degreaser. Then when I had a squeeky clean spa dosed with ahhsome i put the clean filters back in and woh baby.

Its Always best remove the filters from their normal positions until you know what you're up against. You can dump them in the vessel itself (i hang mine on a piece of 1.25 inch schedule 80 pvc pipe) after the bulk of the release is on the sidewalls . Your next purge might not be as dramatic.

The only time i run installed filters while dosed with ahhsome is for the grand finale when you know the release won't clog filters and starve the pumps.
 

Backcountryski

Well-known member
Aug 31, 2019
46
WA
Yea you did the right thing. You can also save some ahhsome dosed water in a bucket for the filters. In fact i do that anyway for wiping stuff down.

In one of my experiments i showed that biofilms accumulate in the filter media by cleaning them first with a degreaser. Then when I had a squeeky clean spa dosed with ahhsome i put the clean filters back in and woh baby.

Its Always best remove the filters from their normal positions until you know what you're up against. You can dump them in the vessel itself (i hang mine on a piece of 1.25 inch schedule 80 pvc pipe) after the bulk of the release is on the sidewalls . Your next purge might not be as dramatic.

The only time i run installed filters while dosed with ahhsome is for the grand finale when you know the release won't clog filters and starve the pumps.
Yea, I did not mean that I wanted to run with the filters installed, only in the tub with the water, but seeing all the gunk that clung on to everything I did not really want that stuff clinging on my filters as I was not sure how hard it would be to get off. Seeing how much came out, I am glad I did not have the filters in the water. Think Ghostbusters level slime, green and super sticky....