Biofilm – Your Hot Tub’s Dirty Little Secret

Much like your body’s overall state of physical health, your hot tub’s cleanliness has as much to do with things you can’t see as it does with the things you can see. Your water’s appearance and the visible surfaces of your tub are only part of the equation. You may see clear water and clean surfaces in your tub (which are good things!), but the state of your spa’s lines when it comes to cleanliness and buildup of undesired debris is also very important. Over time even the most well maintained tubs (in terms of chemical balancing and sanitizing) will end up with a buildup of organic debris, known in the industry as biofilm.
So, what is biofilm? Should you even be concerned about biofilm in your spa? And lastly, what can you do about getting rid of biofilm from your spa?

biofilm AhhSome brochure biofilm pics


Biofilm is a gradual buildup of organic and inorganic material such as bodily oils, lotions, bacteria, water mold, minerals and even dirt which accumulates on the inner surfaces of the lines and multiplies over time. This biofilm eventually can lead to higher sanitizer use, cloudy water, waterline scum lines/deposits, and foul smells that linger no matter how much or how often you shock the tub.

Biofilm Definition

Biofilm Definition


Biofilm begins and progresses over 4 stages: attachment, colonization, growth, and distribution. In the first stage, attachment, this debris simply begins to adhere to surfaces beyond the reach of your normal cleaning routine, such as the inner wall of your hot tub’s plumbing. In the next stage, colonization this biofilm accumulates in the same spot(s) where there is already some attachment. As a colony of biofilm accumulates it begins to grow thicker and starts protecting itself from the effect of sanitizers. It is at this stage we see growth of the biofilm in their little colonies. During the growth stage, biofilm begins to be shielded as it becomes thicker and more resistant to oxidizing chemicals. Then once the colony has reached a large enough size the bacteria and debris present moves to the distribution stage, meaning that biofilm is multiplied and spread to other areas/surfaces. Once these 4 stages have happened, you’ve reached “critical mass” in the fight to keep your tub clean. As mentioned above you may begin to have unpleasant symptoms that are not easily or quickly cured.

Here’s what you can do to get rid of, and more importantly, to prevent biofilm from progressing through its stages and causing problems. If you’re using a typical sanitizer like chlorine or bromine, a regular flush of your spa with a quality cleanser, such a Spa Marvel’s Cleanser, is recommended as often as every 3-4 months. For typical residential hot tubs, one 8 ounce bottle of Spa Marvel Cleanser should be added to the water and run for 24 hours to break down, dislodge and remove all biofilm from the tub. Be sure to remove your tub’s filter cartridge(s) before adding the Cleanser and running the tub, as the whole point is to get the biofilm loose and free floating in the water. Once it has run for 24 hours (you may need to run several cycles), you will want to use a submersible pump hooked up to a garden hose and pump all of the water out. Once the tub is empty, you’ll want to wipe down the shell with a soft cloth and a mild surface cleaner – we recommend Wipe Out!

germ cartoonUnless you’re using a completely enzyme-based sanitizing system, like Spa Marvel (which I highly recommend!), you’ll want to repeat this flush every 3-4 months when changing water. If you do use the complete Spa Marvel lineup of products, you’ll only need to perform this flush of your lines approximately 1 time per year.

So flush your spa’s lines regularly, banish biofilm, and you can rest assured that you won’t be sharing your relaxing soak in the tub with these critters!

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