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About Hot Tub Contamination
decontamination Well-maintained spas are easy to keep clean and healthy.  However, if neglected over time, a persistent contamination problem which is hard to correct may result because of the formation of slimy biofilm containing mold, bacteria, and other microorganisms.

Some signs of problem spas include: slime formation, cloudy water, and foul or musty odors. Another is skin rashes, which may take several days to develop, and which are suspected to have originated from spa use.

If the spa water has become severely contaminated, the plumbing system and filter may be harboring excessive amounts of bacteria in biofilm which may be resistant to your normal sanitizing methods. If you suspect such a problem, have purchased a used spa, or are returning a spa to service after a period of neglect, decontamination procedures should be followed as a precaution, since normal draining, cleaning, and replacement of the spa water may not completely correct it.  Decontamination is also a good practice when switching to a new or alternative sanitizer system.

Fortunately, there is a disinfection procedure which can bring a sick spa back to good health. This corrective action involves three basic phases:

  • Decontamination
  • Water replacement
  • Verification.
Phase 1 - Decontamination

Spa Cover

Replace worn out hot tub cover Thoroughly clean your spa cover, paying special attention to the underside, using Clean All Spray.  Then be sure to seal it with 303 Protectant to help discourage new mildew formation.

NOTE: If hot tub cover is in bad condition or waterlogged, it should be replaced.  A waterlogged cover will likely be infested with mold, mildew, and bacteria, and may continuously inoculate the spa water with more microorganisms. If you need a new hot tub cover, consult the Spa Cover Replacement Guide.

Spa Filters

Hot tub filter sterilization Remove and inspect your filter cartridge(s).  If a year or more old, or in bad condition, discard. Consult the Filter Replacement Guide if needing replacement filters.  If serviceable, clean cartridges using Power Soak Filter Cleaner, per label directions.

After cleaning and rinsing filter, completely submerge the cartridge in a strong solution of Dichlor Chlorine in a clean plastic bucket (use about 1 teaspoon Dichlor in 3-5 gallons of water). Soak for 2 to 4 hours. Also inspect and clean the interior of the filter housing and skimmer.

Hot Tub Vessel Superchlorination

Now that the cover and filters have been addressed, we can focus on the spa itself. Using the dosage table below, superchlorinate the spa water to at least 100 ppm using Dichlor Granular Chlorine which has been first pre-dissolved in a plastic bucket of water.  Pre-dissolving the chlorine will prevent possible damage to your spa's acrylic surface from direct contact of chlorine granules.  (The table is provided since 100 ppm is too high to be measured with test strips).

Spa Gallons

Granular Dichlor - 100 ppm Dosage

100 2 1/2 oz. = 4 3/4 tablespoons
250 6 1/4 oz. = 3/4 cup
500 12 1/2 oz. = 1 1/2 cups
1000 25 oz. = 3 cups

Now raise the water level in the spa to about 1/2 to 1 inch above the normal high water mark.  Circulate the spa water at high speed for 30 minutes with spa cover closed.  Make sure jets are on maximum.  Turn air injector switch on and then off for 5 minute intervals during this process to help disinfect air lines.  If your spa is equipped with an electric air blower, run it for a minute every five minutes.

NOTE: Avoid inhalation of vapors or mist from spa during the decontamination procedures.

Flushing Spa Plumbing System

Spa System Flush Next, and prior to draining, add Spa System Flush per label directions.  Allow water to circulate for an additional 30 minutes, continuing to turn air injectors and/or blower on and off at above intervals.
Spa System Flush is important, as it breaks up and flushes away inaccessible oily deposits, dirt, and other debris from your spa's internal plumbing system. Completes the cleaning process from the inside out.
  Spa System Flush eliminates biofilm from hot tubs

Phase 2 - Water Replacement

Reinstall the cleaned and sanitized filter, or better still, a new filter cartridge.

Refill the spa with fresh water. Now balance the water, paying close attention to Total Alkalinity and pH. Refer to Spa Prep & Maintenance guide.

PreFresh Filling Filter

Fill your hot tub with Cleaner Water

The Pre Fresh Spa Filling Filter reduces many impurities, including odor causing organics. Beginning with pure water reduces demand on your spa chemicals. Highly recommended for well water users or when source water is questionable.  

Do not add your sanitizer at this time, but proceed to Phase 3.

Phase 3 - Verification

The final, and perhaps most important step is verification of decontamination.  Understand that contaminants place a demand on, or deplete free chlorine residual.  Now shock the refilled spa with 10 ppm of Dichlor Granular Chlorine, pre-dissolved in a plastic bucket of water.

Checking for free chlorine residual in hot tub This is approx. 1 1/4 oz. (2 tablespoons) per 400-500 gallons.  Check the spa water with Universal Test Strips to confirm approx. 10 ppm.

Allow the spa to circulate for 8-12 hours with spa cover in place to avoid sunshine degradation of the chlorine level, or circulate overnight if spa is uncovered.

After this circulation period, check the free chlorine level with Universal Test Strips.  If you get a residual free chlorine reading on your test strips, decontamination was likely successful.  If no free chlorine residual is present, excessive demand may still exist, indicating that contamination is still present and depleting the chlorine.  So, if no free chlorine is present, repeat the decontamination procedure.

After successful decontamination has been verified, add the sanitizer system of your choice. (Any residual chlorine will normally deplete in a few days, and is compatible with all of the sanitizer systems that we offer).  Maintaining your sanitizer, and using Spa System Flush with every water change will help prevent the need for a total decontamination again in the future.

NOTE: If residual chlorine is above 5 ppm after verification, reduce it to 3-5 ppm by draining a portion of the spa water and replacing with fresh, or allow chlorine to dissipate naturally prior to using the spa.  If you want more information on the various sanitizer systems available for your spa, refer to our Sanitizer Comparison Guide.

Shake-a-Vac 2

The Easy Way to Vac or Drain

Check out the amazing Shake-a-Vac II self-starting spa vacuum and draining accessory.

spa customers write  Consumer Reviews
Spa System Flush
"I just wanted you to know that your Spa System Flush could be the best chemical on the spa market! I've used it twice in six months to clean out my spa. I get a brown paste around the rim of the tub from the pipes. After cleaning it up & refilling the tub, I've noticed that I have fewer problems with foaming and chemical build up (strong water odor). This has given me more pleasurable hours of enjoyment between water changes."

David Fortlage
Columbia, MD

Spa Depot, The, Spas & Hot Tubs - Dealers, Olympia, WA

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