Hot Tubs and Spas purging and cleaning

Can biofilms grow in storage?


As part of my work outlined in the three-part foundational series “Controlling biofilms in Spas and hot tubs” (see the Hot Tub home page),  I showed the importance of purging any new or stored Spa or Hot tub.  As fortune would have it, I later found myself in a position to test this recommendation under real conditions.  This post outlines  my purge strategy prior to storage, and the results after storage.

Not long after completing the foundational series referenced on the Hot Tub home page, it turned out that  my spa had to be stored for approximately two years, giving me an opportunity to learn more about the effects of storage upon biofilms.  In preparation for storage, I diligently purged the spa with ahh-some, including the filters as the label directions specify.  My reasoning was that purging the spa would  reduce the risk of biofilm growth during storage, and avoid the problems created by manufacturer’s  who wet test their spas prior to various transportation and storage events on its way to the customer.  After purging,  I hired my local spa dealer to winterize the spa and move it into storage.  Their process involved blowing forced air into the jet outlets to displace any water (much like blowing out a sprinkler system in the fall) and then treating the plumbing with ordinary winterizing antifreeze from an RV shop.   The winterizing process worked, as it turned out that the spa easily survived one of the worst  local winters in recent history.

Can  Biofilms grow in storage?

It was the fall of 2017 when hired the same crew to retrieve my spa from storage and install it at my new location.  I was about to find out if the spa had accumulated any biofilm while in storage!  With the exception of the anti-freeze material in the pipes, the spa was preserved nicely, without any visible dust, cobwebs, etc, so I filled it up and prepared to purge.  The influence of the antifreeze was visible, but aside from that the fill water looked great.  Accordingly, I dosed with Ahh-some and grabbed my camera.

Within about 10  minutes, I already had a result:  the familiar appearance of biofilm on the vessel walls.  The amount of material astonished me until I remembered that the spa had been in storage for two complete summers, including several days ‘north’ of 100 degrees F:  What I just released was most likely forming over the previous two summers:

It is fair to ask whether or not this result could be ordinary dust and/or dirt, but further inspection of my spa revealed the answer:  dust and dirt particles end up in the filters, primarily, because they don’t stick to the walls.  Conversely, biofilm ends up all over the place because it sticks to anything.  To further validate this conclusion I looked in the filter compartment:  sure enough, there was evidence there, not only of biofilm but of ordinary particle contaminants that ended up getting trapped in the filter compartment instead of sticking to the walls:


It would take a very expensive, specialized test to prove scientifically that biofilms had formed in my spa during its two-year storage.  However, my  experience has taught me how to detect biofilims by paying attention to the appearance of released accumulation on the vessel walls.  I have learned that biofilms are sticky little devils, and that they always appear on my vessel walls at the waterline or wherever the foam generated by Ahh-some takes them.   I have also noticed how “non sticky” particles end up in the filter compartment instead of sticking to the vessel walls.  These may also be biofilms, but since I have not seen them before in a proven (by sanitizer decay) biofilm release I’ll give these the benefit of the doubt and deem them to be benign.

Accordingly, I conclude that biofilms did im fact form during storage, in spite of my efforts to mitigate this risk.  In addition:

  1. Any spa that is subject to transportation and/or storage delays (especially after wet testing) has a high probability of growing biofilms if the environmental temperatures are right. I remain astonished that manufacturers and dealers continue to either deny this fact or just “look the other way”, preferring instead to feign surprise and offer a “rescue solution” when the customer encounters issues.  I am especially disappointed with Watkins Manufacturing, the makers of Hot Spring Spas — I have reported my results to their manufacturing management team, and my findings were met with clear dismissal of the facts, and a resolve to simply use “rescue” products in the field as needed. I had hoped to influence them to require their dealers to purge upon delivery to the customer, but it was not to be.
  2. All new Spas should be purged with Ahh-some prior to first use.
  3. All used Spas should be purged with Ahh-some at least two times prior to first use
  4. All spas that have been in storage for any length of time should be purged with Ahh-some prior to first use,  even if a purge was performed prior to storage

happy soaking,


One thought on “Can biofilms grow in storage?

Leave a Reply

Your email address will not be published. Required fields are marked *

Back To Top