Hot tub / spa chemicals & water test strips (C) Daniel FriedmanOzone Use in Hot Tubs, Spas, Swimming Pools
Guide to hot tub, spa, pool water ozone treatment

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Hot tub & spa or whirlpool bath chemical & water treatment using ozone generators:

Here we provide a simple table showing how to use chlorine or bromine and other chemicals & treatments to maintain a hot tub or spa, We explain how to use simple test strips to test the level of chlorine, bromine, pH, alkalinity, hardness and other spa or hot tub water properties in order to maintain a safe, sanitary hot tub or spa.

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Use of Ozone as an Oxidizer in Hot Tubs, Spas & Swimming Pools

Freije explains that because their design, use, and water maintenance are different, spas and hot tubs do not function the same nor necessariily present the same hazards as found at public swimming pools.

Spas and hot tubs are not the same as whirlpool baths. Spas and hot tubs are used for recreation rather than for bathing. Many private spas are located outdoors. They are not drained after each use. Most have heaters. The water is treated and filtered.... Spas, hot tubs, and whirlpool bathtubs can provide a fertile breeding ground for many microbes, including organisms that cause disease... - Freije (2000)

The use of ozone (O3) has been promoted by some spa, hot tub and swimming pool equipment & supply producers or vendors as an oxidant or oxidizing agent useful to improve water quality by removing " non-living bather waste such as body oils, cosmetics, sun tan lotions, perspiration, urine" and indeed earlier research (Bataller 2000) suggested that ozone might be a useful component of swimming pool water treatment, and as recently as 2013 (Fernández-Luna) authors have suggested that ozone treatments may reduce swimmer exposure to products of other disinfectants used in swimming pool water.

In the pool and spa water, chlorine acts as a primary disinfectant and it provides the safety residual. Ozone is the primary oxidizer. ... When Ozone is used as an oxidizer in pool and spa water, the quality of the water will improve as problems with combined chlorine compounds are eliminated and eye and skin irritations are greatly reduced. Overall water maintenance and care are minimized as filter runs are longer since clogging greases and oils are broken down, scumline or bathtub rings are kept away or are easily brushed off. The cost of running the pool and spa is lowered as the use of the following specialty chemicals can be reduced: “shock” treatments, scumline cleaners, filter degreasers, clarifiers, scale inhibitors, scents, filter aids.   (Kon, Ultra Pure, un-dated)

Is Ozone all I need to sanitize and keep my spa water clean? The quick answer is “no” but you can eliminate much of your customary sanitizer and shock with a properly functioning ozonator. ... Most hot tubs built in the last 10 years have a built-in ozone generator or are set up so you can add one easily. So, what is ozone and why is it the best thing for sanitizing your hot tub?... Spa ozone is the most powerful oxidizer and disinfectant that can be safely used in spas. It kills all known bacteria, viruses, yeasts and a lot of other things you don’t want to know about... Your spa ozonator needs to be replaced every 18-24 months. (Cunningham, Olympic Hot Tub Blog, 2012)


Perhaps not. The ozone-promotion text above, excerpted from some hot tub and spa suppliers selling ozone generation equipment includes errors and is confusing because sometimes this marketing text even contradicts itself, suggesting that ozone is a sufficient disinfectant methods for hot tubs, spas, pools (it is not), at the same time as indicating that ozone is not "all I need to keep my spa water clean".

Indeed ozone has been used in Europe as a component in water treatment in some public swimming pools. But where used in public pools in Europe the effective use of ozone treatment system for swimming water required extensive additional equipment, steps, and monitoring, such as compressors, dryers, contact chambers and deozonators for treating vent gases and for treating ozone–containing water before returning it to the pool (Wojtowicz 2001 citing Eichelsdorfer 1982, Kurzman 1982).

Watch out: Elliot (1989) demonstrated that typically ozone treatment produced by UV radiation was not an effective spa or hot tub or pool disinfection method.

It is concluded that insufficient dissolved ozone is present for a sufficient reaction time to effect disinfection of these organisms by ozone generated by UV radiation. - Elliot (1989)

Wojtowicz (2001) who has written at length about hot tub, spa and swimming pool water disinfection and treatment has found that in general ozone is ineffective for this application and that in any event it should not be used by methods that might expose the hot tub, spa, or pool users to elevated levels of ozone. That author also found that other claims of the benefits of ozone use in hot tubs and spas were not substantiated.

Ozonating the water while the spa is in use is not recommended because the unabsorbed ozone in the ozonator vent gas can amount to 60 ppm. - (Wojtowicz 2001 p. 147)

A number of UV ozonators have been evaluated and found to be unsuitable for pool or spa use. Although UV ozonator manufacturers typically claim lower chlorine consumption (typically 60 to 90%) and the ability to operate pools and spas at lower chlorine concentrations, no independent data are provided to support these claims.  (Wojtowicz 2001)

Papadopoulou notes that even where potentially effective ozone treatment equipment is installed, its maintenance has been poor and various authors reported that some important pathogens are resistant to the ozone treatment. Rigas, adding poor process design as well, noted the same maintenance problems a bit earlier (Rigas 1998).

The swimming pool with the poorest microbiological quality (THC 500 cfu/ml in 12.1% of the samples, P. aeruginosa counts 1500 cfu/100 ml in 6% of the samples) and the highest prevalence of multi-resistant isolates (73.6%) was the hydrotherapy pool - Papadopoulou(2008)

Resistance to chlorine dioxide and ozone for M. avium was 100- and 50-fold greater ... (Lumb 2004)

Zwiener (2007) offers further details about potential hazards of some swmming pool, hot tub, or spa disinfection methods. But those authors do not suggest ozone as an alternative.

... disinfection byproducts (DBPs), such as trihalomethanes (THMs), which are regulated carcinogenic DBPs in drinking water that have been detected in the blood and breath of swimmers and of nonswimmers at indoor pools.

Separately at OZONE HAZARDS readers will find a series of articles about both successful and un-successful, even dangerous applications of ozone. Also see OZONE GAS EXPOSURE EFFECTS.

Research / References: Ozone use in Spas, Hot Tubs, Pools


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