Controlling Biofilms in Hot Tubs and Spas – part 1


Controlling Biofilms in Hot Tubs and Spas – part 1

My first set of experiments


Residential Hot Tub and Spa manufacturers, as well as consumers, are becoming more and more aware of the presence and impact of a contamination known as biofilms — collections of microorganisms that anchor themselves to the surfaces of pipes, equipment, and even the walls of the vessel itself.   While it is beyond the scope of this article to discuss the nature of biofilms themselves, I will highlight the following points of interest to the present effort which are generally understood and accepted in the industry, established in the literature, and proven in controlled studies (references at the end of this post):

  • Biofilms are living microorganisms which self-generate and adapt to the environmental conditions in which they live
  • Biofilms can contain and provide safe harbor protection for many types of organisms including bacteria (e.g. Legionella and Pseudomonas), fungi and algae.
  • Biofilms form inside pipes and equipment, even when not detected on the surface of the vessel walls.
  • Biofilms have be shown to accumulate in the presence of 1-3pm Chlorine

With awareness of the above facts emerging, spa manufacturers and consumers are faced with the same underlying problem but have different reactions to it.  For example, when consumers are made aware of the unseen accumulations in their Spa, they typically take whatever action is necessary to purge and/or maintain their vessels and they are willing to purchase something to help them accomplish this goal (Indeed, the industry has responded with a plethora of retail products to profit from this).  Manufacturers, retailers, and even dealer service departments,  on the other hand, show a reluctance to acknowledge the nature of these hidden contaminants, perhaps because they want to avoid the perception that a new Spa or Hot Tub could potentially be contaminated upon delivery or they want to avoid creating unnecessary alarm in the minds of consumers.  Finally, there is a handful of private spa owners who are comfortable with old-school best practices and who are disinterested in the newest information on this subject, preferring instead to remain “blissfully unaware” because nothing bad has happened to them.  Yet.  You see, I used to be in this category.

Experimental method and  motivation

In addition to evaluating a handful of purge products for their effectiveness, the present effort brings clarity to the following questions:

  • Should the consumer be concerned about biofilms even when proper water maintenance procedures are followed?
  • Is clear water sufficient evidence that biofilms are not present or problematic?
  • What are the signs that biofilms may be forming in the Spa?
  • Can a chlorine shock treatment remove biofilms?
  • Can biofilms form in the filters even when they are maintained properly?
  • Can biofilms be present in brand new hot tubs and spas as delivered by the manufacturer or local retail store?


I have successfully maintained a personal Spa since the early 1990’s, using traditional sanitizer and water balancing products, shock treatments and frequent, careful testing.   The sanitizer I became familiar with, and which my family grew to prefer, was bromine —  established in my Spa using a combination of Sodium Bromide salts and granular “dichlor” chlorine as the oxidizer.  Occasional shock treatments were not uncommon, especially when planning to leave the Spa for several days at a time at which time I would dose to very high levels so that the sanitizer level would not drop to zero before returning home.

In the mid-1990s, I purchased an outboard UV-based ozone generator as a sanitizer supplement and to assist in the oxidation of sodium bromide in order to advantage water maintenance during “away time” (did you know that ozone makes bromine?).   Unfortunately, the system could not maintain a positive bromine level under no load conditions, as I had hoped;  I presumed this to be due to insufficient ozone generator output.

During the summer of 2013, I purchased a new Hot Spring “Grandee” spa with an integrated corona discharge ozone generator, expecting greater ozone output and an improvement in the rate of bromine decay in the water under “no load” conditions (Corona discharge, as a method of generating ozone, generally produces higher concentrations of ozone than does the UV method).   The value proposition of Ozone in a bromine spa is very compelling:  Not only does it oxidize contaminants directly, as a supplement to the sanitizer,  it also oxidizes sodium bromide into bromine, contributing a small amount to the sanitizer level itself!

Upon installation of the new spa, however, I found that my sanitizer decay rate still did not meet my expectations,  even after shocking with very high sanitizer levels (“SLAM”, or “Shock Level and Maintain”) according to generally accepted best practices.  I continued to use the spa, testing rigorously and treating as needed to insure clear, properly sanitized water. Despite my efforts (and a relatively low bather load of 2-3 hours per week) the water became increasingly difficult to manage, and I ended up changing my first fill water after only 2 months.

To my astonishment, changing the water and SLAM’ing per standard guidelines did not help.   I finally realized that my brand new spa, with integrated corona discharge ozone, required the same or even higher level of maintenance as did the old spa — only this time I couldn’t blame it on being gone too long, not dosing high enough, or a weak ozone generator.   I started to become suspicious of biofilms, but initially dismissed the idea because my spa was brand new.   Finally, after fighting both first and second fills, I started to pay attention to the obvious:  My new spa had been wet tested at the factory and subjected to various storage and transportation delays.  It must have arrived with an organic contaminant (such as biofilms) already established and growing.  The only remedy was to purge.

Choosing a purge product

Anxious to solve this problem with a purge product, I performed an industry scan which revealed a set of products with particularly attractive marketing statements and claims for certain victory.   I couldn’t test all of them so I arbitrarily limited my experiments to the ones that caught my attention:

  • SeaKlear System Flush (“super-cleans plumbing systems of hot tubs and whirlpool baths”)
  • Silk Balance Clean Start (“Cleans organic deposits from plumbing”)
  • Aquafinesse Spa Clean (“thoroughly cleaning your spa from the inside out!”)
  • Natural Chemistry Spa Purge (“Restores spa plumbing to original condition”)
  • Unique Solutions  Ahh-Some (“Caution:  buildup may contain biofilm and other contaminants”)

The last product in the above list, Unique Solutions, “Ahh-some”, claimed superiority in head-to-head tests with other products, so I decided to challenge this claim by experimenting on my own spa.  My working hypothesis became the following:  “Ahh-Some will visibly remove more material from pipes and equipment compared to the other products”.  This hypothesis could be tested easily enough, I reasoned, by purging with one or more of the competing products before purging with Ahh-Some.  If Ahh-Some released material after the others had done their work, I would then declare the hypothesis validated.  Otherwise,  I would declare the hypothesis to be false and the Ahh-Some claims to be advertising hype.

The following describes my experimental journey, including steps taken, results obtained, and the conclusions I reached.

Experiment #1:  SeaKlear “system flush” vs Unique Solutions “Ahh-Some”

As I prepared to drain my spa for the second time, I noted that my water was in bad shape – it had “gone cloudy” a few times (while I was away), and even after shocking and restoring water clarity, my sanitizer demand still remained too high – on the order of 30% or more, over 24 hours.  Especially with ozone in use, and with Sodium Bromide salts in the water, a 30% decay rate is very strong evidence that something is consuming the sanitizer at a higher than normal rate.

I decided to give SeaKlear “System Flush” a first crack at my spa with the known-bad water.

SeaKlear “System Flush”

Before draining the known-bad water, I removed the filters and added an entire bottle of SeaKlear “System Flush” to my 500 gallon spa (this is a dose recommended for 800 gallons).  I ran all jets and the water feature for approximately 45 minutes, although the air intakes were turned down to minimize foam.  Within a few minutes, I noticed a small amount of brown-colored deposits along the waterline and inside the filter compartment – convincing evidence that the product was doing something good.  I was not able to determine conclusively that actual biofilms were removed (which would have required expensive testing) –I simply assumed that if the product was depositing such material along my waterline, it must have come from either the known-bad water or the pipes or both.  I took note of how much material I saw along the waterline, let the spa sit overnight and  then drained, cleaned, and refilled it the next day after confirming that no new material had been released.

With fresh, new, water in the spa I repeated exactly the same process with a 2nd bottle of System Flush, just to give this product ample opportunity to remove what it could.  This treatment produced no result – I obtained perfectly white foam and no residue along the water line, from which I concluded that the product had done all of its work on the first purge.   Again, I let the spa sit overnight and, after confirming that no new material had been released, I drained, cleaned and refilled again in preparation for the next step.

Add Ahh-Some

Now it was time to give Ahh-Some a chance to work.  This time, the water was new, clean, and treated with a stain and scale control product just to insure that metals or calcium would not confound the result.   To further disadvantage the Ahh-some product, I dosed with just over half of the recommended dose.

Instantly upon dosing with Ahh-Some,  I saw new brown-colored deposits accumulating on the vessel walls –easily 10 times a much material than the previous two applications of the SeaKlear product had released.  This result was convincing:   $6 worth of  Ahh-some had released more material when added to the (new) water than $15 worth of SeaKlear had removed when added to the original (tired, bad) water.

With this success, I put my filters back into the vessel as the Ahh-Some instructions suggested.  Not in their normal positions, but just floating around on top of the water so that the Ahh-Some dosed spa water would benefit them as well.   The water flow in the spa was so strong that the filters kept blocking access to the skimmer weir, and I resolved in the future to use a piece of PVC pipe to control their movement.

I was left wondering if the SeaKlear had actually removed any contaminants and/or biofilms from the pipes and equipment, or just precipitated contaminants out of my water, which I already knew was bad.  Not knowing how the product works,  I decided to give SeaKlear the benefit of the doubt, but the experimental result was clear:  Ahh-Some had clearly removed material from my spa that SeaKlear failed to touch.

Experiment #2:  Ahh-Some versus three other products

The first experiment had produced an astonishing benefit:  My sanitizer demand returned to normal, and my ozone generator was now able to maintain a detectable level of bromine under no load conditions, at least as long as no stray spiders or other organic material from nearby trees entered the spa.  This was convincing evidence that biofilms were in fact the root cause of my original problem, and that Ahh-some had provided the solution.  Moreover, this result confirmed that biofilms had arrived along with the spa as delivered by the factory.

After completing the first experiment, my water maintenance turned out to be a breeze and my water was still clear and well-balanced nearly 6 months later.   However, the following questions were left unanswered:

  • “Can biofilms form even with properly maintained water?”
  • “Are there other products that can perhaps compete with Ahh-some in the removal of contaminant material, including biofilms?

To help answer these questions, I performed the same type of experiment as I had with SeaKlear, only this time I evaluated three new Ahh-Some competitors.  Working from the same operating hypothesis (Ahh-Some will visibly remove more material than the other products), I decided to purge my spa with all three of the other products first before giving Ahh-some a chance to work — and to photograph the evidence!

This experiment was different in that, while my water was six months old, it was clean and well maintained:  I was not trying to solve a water maintenance problem!   To document my starting point, I took the photos shown below:  The water was clear, although it didn’t “sparkle” like new water does.  My filters were also clean and in good shape.


Silk Balance “Clean Start”

My first step was to treat the old (but well maintained) water with Silk Balance, “Clean start”, following the label directions exactly as printed.  I removed my filters and placed them into a solution of traditional filter cleaner (this will become important to the story later on…).  Per label directions, I dissolved the (rather abrasive) Clean Start granules into a separate 5-gallon bucket of spa water.  I threw out approximately 1 Tablespoon of the product (less than 1%) which did not dissolve, in order to protect my pumps.

With the filters removed and jets running, I added the Silk Balance solution and grabbed my camera.  Below is a photo of my spa running with “Clean Start” present in my 6- month old well-maintained water.  I observed a little foam, but that’s about it.  Nothing formed on the vessel walls or inside of the filter compartment.  I even photographed the side of the vessel wall where contaminants normally accumulate (second photo below).  There was no accumulation.

After letting the product work for about 30 minutes, per label directions, I decided to turn the jets and circulation pump off to see if any material had accumulated.  The foam subsided but there was no evidence that any contaminants had been removed.  I even let the spa soak for another hour, well beyond the label directions, with the circulation pump running:   A small amount of foam appeared on the surface, but there was no evidence of any contaminant release as shown in the photo below:

These results showed that the Silk Balance product released nothing visible –  I was starting to feel good about my spa maintenance skills!    I drained the spa according to the label directions, then filled again with fresh water, in preparation for the next step of my experiment.

Below is a photo of my spa and filter compartment filled with fresh water, in preparation for the next test.  Note the color and clarity improvement in the new water compared to the 6- month old water shown at the beginning of this experiment.  This result is clearly due to the new water itself, and had nothing to do with the previous Clean Start purge, which released no contaminants.


Aquafinesse “SpaClean”

At this point I was starting to question the value of purging a well-maintained spa filled with new, clean water, but since my working hypothesis was, “Ahh-Some will visibly remove more material than the other products”, I decided to continue the experiment with a product from Aquafinesse, called “SpaClean”.

I dissolved the Aquafinesse,  “SpaClean” puck in a separate 5-gallon container of spa water, just as I had done with the “Clean Start” product before.  I found that dissolving the “puck” was only slightly less difficult than dissolving the Clean Start granules.  After pouring the dissolved product into my spa, I opened up all the air injection knobs to generate as much agitation as possible, and ran the pumps three times, 20 minutes each time, over the next 24 hours per label directions.  As there was no visible result after 24 hours, I extended the test for another 24 hours, and still obtained no result.

The next two photos show my spa running after a 48 hour Aquafinesse treatment.  There is no evidence of the product doing anything useful, although it did generate a little foam.

With the above two results I was beginning to wonder if the Silk Balance and Aquafinesse products  were really that useless, or if perhaps my Spa was just exceptionally clean!  At this point in the experiment, I favored the later conclusion — after all, the spa was well-maintained, trouble-free and filled with new water, so what made me think that purging would do anything useful?  For interest’s sake, I checked the quality of the water “at rest” (jets off)  when treated with Aquafinesse:    It was remarkably clean, appearing very much like my 6- month old well-maintained water at the beginning of this experiment.  The Aquafinesse product produced less foam than the Silk Balance, and produced the same result:  Nothing.

The photo below shows that the only impact of the Aquafinesse treatment was to make my new fill water look like properly-maintained 6-month old water:

I should point out that the first product (Silk Balance “Clean Start”) is nothing more than ordinary Borax in a really expensive container – it is the very same compound sold under the “20-Mule team” brand at the grocery store.   Borax may be a good general purpose cleanser, but it did not release any (visible) contaminants from my water, nor did it release anything from my pipes or equipment.  In fairness to this product, subsequent to this experiment I later learned that “Clean Start” is not marketed for biofilm purging,  in spite of it’s “cleans organic deposits” claim.

The second product (SpaClean) looks and behaves the same as Borax, but I had no opportunity to verify the actual ingredients.  It did not have any chance to precipitate contaminants out of the water itself (because the spa was filled with new water), but it should have released contaminants or biofilms lurking in the pipes or equipment, if indeed such material was present.   It did not.

I kept reminding myself that normal people don’t purge their spas unless there is a known problem, and  yet I was attempting to purge a well-maintained spa filled with new water.   It felt rather silly, but this was precisely the approach required to answer the important questions of the experiment:  I wasn’t interested in a product that cleaned the obvious; I wanted a product that would clean what might be hiding.

Why are these products so successful in the market place if they do so little?  Did no contaminants or biofilms form while I was properly maintaining my spa over the past 6 months? The answers to these questions still eluded me, as I drained, refilled, heated, and balanced my water in preparation for the next test.  For documentation purposes, here is a photo of my spa with new, balanced and heated water.


Natural Chemistry

Natural Chemistry “Spa Purge” is an enzyme-based product – a brownish colored liquid with a strong “brackish” appearance.  The label directions are clear that foam may accumulate quickly, and suggest only 5 min of “Jets on” time.  I turned off all the air intakes, poured the bottle into my 500 gallon spa, turned on the jets, and grabbed my camera again.




The label was right:  within 5 minutes, there was so much foam I had to turn the jets off to avoid treating my lawn with this stuff.   The amount of foam quickly approached the height of my water feature, as shown in the next photo, but appeared to release no contaminants or biofilms.  Apparently, this manufacturer has determined that foam is more effective than water/air agitation for the purpose of releasing contaminant material.  Or maybe just more impressive:  The next two photos show the extraordinary foam production of this product:







At this point, the foam effect was so prominent, I realized that if any contaminants or biofilms were to be released, they might very well be under the surface of the foam instead of on top! Accordingly, I let the spa sit for an hour to let the foam calm down.  In the photo below you can see that a “foam dome” appeared over the ozone injection/heater outlet at the bottom of my spa.  The color of the water has changed dramatically but there is no trace of any organic accumulation on the walls.

At the four hour mark I finally saw a result.  Look closely at the spa surface near the waterline in the photo below:    A tiny amount of material has been released — something HAD formed over the past 6 months!

The Spa Purge label directions specified an “overnight” soak, so I decided to leave the spa (with circulation pump running) for  20 hours.  Nothing new appeared the next day, except for impressive amounts of foam even with the jets off, as shown in the photo below:

After the 20 hour soak, I started to drain the spa to more thoroughly expose the site where released material had accumulated.   I did not notice any new material:   The product had performed its work within the first four hours.

The amount of material released by the Natural Chemistry product was very small (I would say less than 1/100th of the material that Ahh-Some had released in the first experiment), but definitely not zero.  After wiping up all the visible material I could find, I drained, filled, balanced, and heated the water again in preparation for testing Ahh-Some.

Here is a photo of my spa with new/clean water, after purging with all three products:  Silk Balance, Aqufinesse, and Natural Chemistry. I was now at the 3,500 gallon milestone, and ready to see if Ahh-Some would release any material that the others missed.


With the filters removed and new/balanced water in the spa, I fired up the jets again and added 5 tsp. of Ahh-some, the prescribed amount for a 500 gallon spa.  The product produced a lot of foam, so I started to compare this with the amount produced by the Natural Chemistry product:   I determined that the amount of foam produced by Ahh-some, in 30 minutes,  was about 70 percent of what Natural Chemistry produced in 5 minutes.  Here is a photo showing the spa dosed with Ahh-some and with jets running, at the 30 minute mark:

The next photo shows another view of the foam. If you look closely at the base of the water feature, you can see that a white residue has started to form on the vessel wall. Although it is hard to see in this photo, the white stuff blends in with and is riding on top of the foam.

I shut down the jets (to let the foam settle) to get a better look at the vessel walls, and was astonished to see a significant accumulation of this residue.  Look at the photo below — that’s the stuff that was riding on top of the foam!

This material was definitely not standard body oils/lotions or grease.  It was white, and had a sticky, flake-like nature to it, when dried.  I reminded myself that this was a new spa:  could this be a byproduct of, or contamination produced by manufacturing?  I also reminded myself that three other purge products had been used previously:   Ahh-Some could have either removed what was left behind by the others, or the action of the other products could have discolored or influenced the appearance of this white material without actually removing it.  In spite of my analytical nature I decided not to figure it out:  The important conclusion was that Ahh-some had removed it.  I also concluded that the other three products did not, of themselves, introduce contaminants.  Had they done so I would have seen some evidence on the vessel walls, which I did not.

Inside the filter compartment, the nature of the white material released by Ahh-Some was apparent as well:  The foam was not uniform in texture, and had formed globs of material riding on top of the water surface, as shown in the next two photos:

I now had a clear result:  Ahh-some was removing gunk that the other products failed to touch– and large amounts of it too.  Whether that gunk was influenced by the other products didn’t matter to me.  What mattered was that Ahh-Some released it.

The absence of a significant brown-colored contaminant release still intrigued me, and I could not shake the thought that such material might still be present, hidden or otherwise protected, perhaps by whatever this white sticky stuff was.  To test this, I decided to drain the spa, refill, and purge again with Ahh-Some.  Sure enough:  The 2nd Ahh-some purge released more contaminants of the more traditional appearance!  Note the accumulation on the far wall in the photo below:

Below is a close-up photo of the new accumulation.  This material was different in appearance, compared to the previous white sticky residue, and had the more common yellow-brown appearance.   The foam itself took on a more normal appearance as well.

Clearly, the second Ahh-Some purge had produced a new result, and  I decided to let the spa sit overnight to see if additional material would be released.  it turned out that material continued to accumulate on the vessel walls over night, as shown in the next photo, convincing proof that  I had some serious nasty stuff hiding in my equipment.  Here is a photo showing the inside of my filter compartment, after an overnight soak:

Apparently, this brown-colored material had been lurking under the surface of the white material that was released by the first Ahh-Some purge. Certainly, it was impossible to know if the white material had been forming over the past six months, or if the previous three purge products influenced its appearance, but my conclusion was the same either way:  Whatever this stuff was, I didn’t want it in my spa, and Ahh-Some was the only product capable of removing it.

I now had to adjust my experiment yet again.  Had the 2nd purge of Ahh-Some removed everything the product was capable of removing?   If the white material had protected or otherwise prevented release of the brown material, what kind of material might still remain?  These questions were impossible to answer without purging again.   Accordingly, I drained the spa, refilled and purged for the third time.

Here is a photo of my spa in its 3rd Ahh-Some purge.  No new material was released!   I did see a slight discoloration in the filter compartment (evidently a small residual from the previous purge) which I easily collected with a micro fiber cloth.

I now had satisfactory answers to the above questions: Two treatments of Ahh-Some had successfully purged my spa of whatever remained after purging with the previous three products.   In addition, I had a conclusive answer to a question which I have actually heard expressed by someone who doubted the effectiveness of purge products:

Q:  Had Ahh-Some actually introduced new contaminants that it now released, just for visual impact?

A:  Without question, NO.  If Ahh-some was capable of introducing contaminants just for visual impact, it would be impossible to achieve clean spa with no newly released material, while dosed with the product.

Here is another photo of my squeaky clean Spa, dosed with Ahh-some for the third time, releasing no new material.   Two Ahh-Some purges had done the trick, and I had achieved the cleanest spa known to man.

Encore Performance

Having established the superiority of Ahh-Some, compared to the other four products, there was one question I neglected to raise earlier in this experiment:

So you think your filters are clean? Think again.

Recall that my filters had already been cleaned with a traditional filter cleaner/degreaser product during the previous Silk Balance purge (I used SpaGuard® filter cleaner).    However, given the success of Ahh-some in the spa itself, my mind naturally raised the question:  Had my filters also accumulated material, perhaps even biofilm, which the filter degreaser left behind?   During the first experiment (SeaKlear vs Ahh-some) I had cleaned my filters with ahh-some (put them into the dosed vessel) but never validated that this procedure was any better than the traditional filter cleaning method.

To answer this question, I installed my clean filters into their normal positions.  Normal positions!  This goes against the Ahh-Some label directions, which plainly say to remove the filters — the reason for this is that the gunk released by Ahh-Some is likely to plug up the filters and starve the pumps of water.  But in this case I had already achieved a clean spa, so in this step I would be deep cleaning the filters themselves, not the spa.  Also —  please note that I do not recommend this step for paper filters, which are considerably less durable than my ceramic filters!

With my ceramic filters now installed in their normal positions, and my spa still dosed with Ahh-Some and releasing no new material, I fired up the jets and grabbed my camera again.  Instantly, new accumulations began to form, as this photo (below) of my filter compartment shows.  This material had been lurking in my filters!

As the minutes passed, the new (but small)  accumulations released from the filters appeared on the vessel walls as well, as shown in this photo:

Since my filters had been cleaned already by an industry standard filter cleaner/degreaser, what does that say about the material now released?   Especially given the effectiveness of Ahh-Some, I reached an unmistakable conclusion:  This result is strong evidence I had just removed biofilms from my filters, although I didn’t prove that with a sanitizer demand test:  The important thing was that Ahh-some had released new material.  Good thing I had chlorine in the water!    Now my dilemma was what to do with this material?  Should I drain again?   I adjusted my experiment again with another working hypothesis:  The amount of material released from my filters was small, compared to previous contaminant releases.  To test this hypothesis, I decided to wipe up the material released from the filters with a soft, micro fiber cloth, rinsing frequently in a separate solution of Ahh-Some.    This technique worked:  after several wipe-rinse-wait cycles over approximately 30 minutes time, I achieved a clean spa with filters installed, still dosed with Ahh-some.

Below is a photo of my spa, dosed with Ahh-Some and with filters installed into their normal positions, showing perfectly clean water.  THAT is a clean spa!


I had used over 5,500 gallons of water in the experiment and nearly $100 worth of various chemicals, but I now had answers to all of my remaining questions, which I present in PART 2



This paper: by D.M Goeres, T Palys, B.B Sandel, and J Geiger presents a plausible data suggesting that bacteria can adhere to surfaces in the presence of 1-3ppm FC,

Paula Dreeszen, “Biofilm.  The key to understanding and controlling bacterial growth in automated drinking water systems”, second edition (2003)



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