Hot Tubs and Spas purging and cleaning

Pushing the limits of Hot Tub Serum

In the foundational materials on this site (see the Hot Tub  home page) I highlighted that biofilms can survive chlorine concentrations of 1-3ppm — levels that some authorities still promote for regular use.  In addition to ahh-some as a purge product, Hot Tub Serum (or “Serum Total Maintenance”) gives us another tool in our toolbox to combat the problem of biofilms and “bad guys” in general.   Here are the major points of interest that I have established to my own satisfaction via experimentation:
  1. The useful drain interval of hot tubs sanitized with “dichlor” (granular Chlorine for Hot tubs)  is limited by the rising accumulation of Cyanuric acid (CYA) which renders Chlorine increasingly impotent as the sanitizer is added on a regular basis.  I’ve been able to confirm that “Hot Tub Serum” is immune to this problem, and continues to attack bad guys no matter what levels of Chlorine and CYA are present.
  2. Without automatic sanitizer dosing (a floater, for example) it is not a trivial matter to keep Chlorine levels from dropping into the 1-3ppm region or below, where research has shown biofilms can survive and even grow.   In my experience, Hot Tub Serum is a profoundly effective solution to this problem(when used as directed), as it continues to attack bacteria that would normally survive under these conditions.  It turned out this was just too easy to prove — I let my Spa go to zero chlorine on a number of occasions and each time Hot Tub Serum not only kept my water clear for DAYS (with no chlorine), it also attacked the bad guys and left the evidence thereof on my vessel walls!
  3. Hot Tub Serum acts as a sanitizer supplement, working alongside chlorine and even absorbing some small portion of the bather load.  This produces an astonishing “no bather load” sanitizer decay performance, shown in the graph below.  To produce the data represented by the graph,  I let my spa go un-used for a couple of days (to insure there was no bather load), and then dosed to about 5ppm Bromine. I then left the spa, covered and unused, and measured bromine levels over time (the X-axis in the graph is in hours, and extends beyond 6 days).   The upper (dark) line represents the sanitizer decay rate with Hot Tub Serum in the water. The lower two lines represents the decay rate without Hot Tub Serum in the water.
  4. Hot Tub Serum is NOT a disinfectant or sanitizer in its own right — and neither is it an oxidizer but it DOES work synergistically with your existing sanitizer program.  For me, this means using Serum along with chlorine or bromine (whatever suits me at the time.  I use both).  The manufacturer has stated that Serum works by breaking down bacterial cell walls, producing a residual  by-product that ends up in your filter.   In poorly maintained spas using Serum Total Maintenance for the first time, the result can be a rather dramatic accumulation of material on the vessel walls or inside the filter compartment.   This tells me that there is likely a coagulant of some sort in this formula.

Pushing the SERUM limits

Now for the fun part.   My next objective was to find out just how long my water would survive with only HOT TUB SERUM present in the water — and no Sanitizer.   I would not be testing the sanitizer decay rate I would simply measure the amount of time it takes for the water to go bad, with zero sanitizer present.   Mindful of the manufacturer’s claims and the label directions (I was about to go well beyond the intended use, with water un-protected by a known sanitizer), I wasn’t sure what to expect but there was only one way to find out:  I used the spa as I normally would, just to introduce a bather load,  but I did not add any sanitizer after getting out.    I left the spa unused, as an experiment to see what happened.   Here’s what happened:

1.  After two days my water was still clear and my sanitizer  level had only dropped from 5ppm to 1.2ppm — that’s a little steeper of a sanitizer decay rate than a normal “no bather load” would produce, but I had to remember that I had just introduced a deliberate bather load to start this experiment — so this decay rate was expected.

2. Over the next day my sanitizer finally reached zero and I “started the clock” — observing  the condition of my water over time.  What I discovered was astonishing:   After 12 hours of no sanitizer, my water was still crystal clear.   After 24 hours — crystal clear.   36-hours — crystal clear.  48 hours  — still crystal clear!  Finally, at 50 hours I went to bed.    Sometime during the night, between 50 and 58 hours without any sanitizer, my water turned bad with the characteristic cloudiness of un-sanitized water.

3.  If that wasn’t fun enough I decided to go one step further:  Having finally obtained bad/cloudy water, I now had the opportunity to see what Serum could do to help the recovery process, all by itself.   I dosed my spa with approximately twice the manufacturer’s recommended weekly amount but added no sanitizer or shock treatment.   Within one hour I started seeing small accumulations of material on my vessel walls and in my filter compartment — as shown in the photo below.  I decided to wipe up this residue with a micro-fiber cloth (essentially supplementing my filters).  I also ran the jets for a few minutes to aid this process.

Here is my filter compartment after adding Hot Tub Serum to known-bad water:  Notice that it produced a “mini purge” by depositing material on the vessel walls.  Using Hot Tub Serum in this manner is WAY outside of the manufacturer’s intentions, but it allowed me to see what it was capable of doing    At the 24-hour mark, I observed a striking improvement in my water — still with NO SANITIZER!  The photo below shows the Before (right side, bad water after 50-58 hours) and the After (left side, 24 hours after dosing with  Hot Tub Serum).


This is an astonishing result:   The Hot Tub Serum  formula had restored water clarity to about 80% in 24 hours — without the aid of any sanitizer or shock.  That last 20% of water clarity (and safety — remember this is an experiment) would have to come from a real sanitizer such as chlorine or bromine.

Some have suggested that this performance is due to the water clarifiers present in the ‘Serum. Others think I am promoting something dangrous ,when I am only reporting results.  Have you ever tried to clean up bad water just with the use of a traditional clarifier?  The water clarifiers I have used don’t leave biofilm deposits on the vessel walls :-).

The “Whole” is greater than the “Sum of the Parts”

No, I will not go without a real Sanitizer,  but this experiment did convince me that the combination of Hot Tub Serum and Chlorine/Bromine is a profound success. To prove this out even further,  I then added a shock-level of chlorine, and achieved full water clarity in approximately 8 additional  hours.    Normally, such a rehabilitation would require a “Shock Level And Maintain” (SLAM) regimen but this result required only one sanitizer application (the “Shock Level” without the “maintain”).


Additional Conclusions

At this point it is  wise to remember that Hot Tub Serum is a companion product to and does not replace a sanitizer.  For a while, that sounds just like the marketing claims of enzyme-based products (such as Spa Marvel).  Serum is not a sanitizer — it is an EPA registered biocide when used as directed (9% “ADBAC” for the chemists among us).  That means it kills bad guys  — when pushed to its limits it profoundly helps the water recovery process.

happy soaking,


4 thoughts on “Pushing the limits of Hot Tub Serum

  1. Thanks for the great information. What products would this replace in the traditional start up kit most spa companies send you home with? Just clarifier or would there be others? I’ve been using the Frog @ease, not real happy with it. I’m considering switching to the Frog Serene with Bromine but dang, $$$! My son has super sensitive skin. Looking for any suggestions. Thank you!

    1. I haven’t used a clarifier in years, and prefer a minimalist approach. spa store shelves are awash with products to fix everything known to man, and most of those problems are simply due to biofilms. Regular purges with ahh-some (or use their new “Aqua Clarity product that is the bees knees) eliminates the biofilms and a host of other problems including pH control. just keep up on the chlorine/bromine treatments and you’re golden

  2. First, thank you for your clear, scientific approach and explanations in your product reviews/comparisons.

    Can you explain appropriate use of shock for a properly balanced hot tub when using Hot Tub Serum? Is weekly shock needed when using HTS if a 3-5ppm bromine level is maintained? Is MPS or dichlor shock more appropriate for a bromine spa? Is there a best time to add shock in relation to HTS, or does it not matter? Also, I’ve been adding bromine granules after each use. Is shock more appropriate?

    Overall, while I don’t understanding how best to utilize shock with HTS, water quality has been very good shocking once per week when I add HTS.

    1. I’d suggest that the best way to approach this question is to consider that Serum and Bromine are differnet tools that attack different problems. That means shock the water as if you were not using Serum. weekly is good. I usually alternate between MPS and dichlor. straight dichlor raises the bromine level to shock level (as you would expect) but doing the same with MPS introduces some additional happiness in that the conversion from MPS to bromine happens differently and slower, so that there is MPS action that occurs before the conversion is complete. these “quat” based maintenance products like HTS are spectacular at controlling biofilms but do not replace the sanitizer itself for attacking pathogens like pseudomonas and a host of others. Also, while crystal clear water is very satisfying, HTS will easily acheive this even with zero bromine in the water, which means you still have to shock.

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