Spa Water Chemistry

pH & Total Alkalinity:

The topics of pH and total alkalinity are inter-related and are key parameters (factors) in the overall pool water chemistry. pH is the relative acidity or alkalinity of the water. The pH scale goes from 0 (most acidic) to 14 (most alkaline) A pH of 7.0 is neutral. Ideally, spas and hot tubs should be maintained in the 7.2-7.8 range for a variety of considerations: sanitizer effectiveness, bather comfort, corrosion, cloudy water and scaling. Total alkalinity is a measurement of the total quantity of alkaline materials present in the water. Low TA allows for rapid pH fluctuations makes pH control more difficult and can contribute to corrosion. High TA makes pH adjustment more difficult and can be a contributing factor in cloudy water and scaling. A TA range of 80-120 PPM is considered optimum. Control of the spa or hot tub water chemistry is necessary to assure optimum pool water quality.


Calcium Hardness:

Calcium is a naturally occurring mineral that is frequently found in high concentrations: such water is called “hard” water. Calcium hardness is one of the important spa and hot tub water chemistry parameters and its control is important to help assure proper water quality. Calcium problems do not normally impart a color to the spa water, as does the presence of metals such as iron and copper. The preferred range for spas and hot tubs is 80-200 PPM. Low levels of calcium can lead to possible corrosive water conditions. Chemicals are available to raise the calcium hardness, as might be necessary. High calcium hardness levels, especially above 400 PPM, can lead to possible water clarity problems and scaling conditions. Various chelating or sequestering Mineral Treatment Products are available to help deal with the problems associated with high calcium hardness levels. Spa or hot tub calcium hardness levels can be determined by a simple water analysis. This is especially important with well water, as other problematic minerals might be present and could require treatment. Spa Water Magnetizers, also known as Magnetic Water Conditioners have been reported to help reduce and eliminate scale formation, by inducing a positive electrical charge in the water passing through the return lines.


Mineral Problems:

Mineral content in spa or hot tub water can lead to a variety of problems: staining of the underwater surfaces, discoloration of the water and corrosion. Control of trace minerals and maintaining a proper overall spa or hit tub water chemistry is important, to help assure optimum water quality. Minerals such as iron, manganese and copper are the principal offenders. Iron and manganese can occur naturally in water, especially well water. It is the oxidation of dissolved heavy metals that can cause the spa staining and water discoloration problems, upon the addition of oxidizing spa chemicals. Copper is rarely found in municipal water supplies and usually finds its way into spas and hot tubs as the result of corrosion of the copper heater core or copper plumbing. Treatment of the resultant problem is usually possible with the proper techniques and chemicals.


Spa Water Testing:

Proper water management starts with the analysis and balancing of the spa or hot tub water. Tests such as pH and sanitizer need to be performed by the spa owner, on a frequent or daily basis, depending upon the sanitizer choice and usage conditions. If Chlorine is used, it should be tested by a method that measures Free Chlorine, as it is the most important. Tests such as total alkalinity and calcium hardness are performed occasionally and can be done by a spa owner or dealer. Tests for heavy metals such as iron, manganese or copper should be performed at the initial filling or at the first indications of spa water discoloration or a spa surfaces staining problem. These tests are usually performed by a spa professional. Maintaining or balancing proper spa or hot tub water chemistry is important to help assure optimum water quality and to maximize the “hot water” experience.

Spa Water Quality

Cloudy or hazy water is one of the most frequent problems that a spa or hot tub owner will encounter. There is no one cause of cloudy, murky, milky, gray, hazy or dull spa or hot tub water problems: suspended insoluble particles, dead algae, organic debris, poor or inadequate filtration, inadequate sanitation, poor water chemistry, poor source water quality, vandalism and more, all have to be factored into the treatment. A spa water color problem is frequently with presence of heavy metals and may or may not be associated with cloudy spa water conditions. Foamy spa conditions, resulting from the aeration of soaps formed by body oils and cosmetic residues reacting with the natural alkalinity of the water, can detract from optimum water clarity. Most spas and hot tubs do maintain clear water conditions, with good water clarity. For those occasional problems, many chemical products are available that help to restore the water quality to crystal clear.


Algae, Mold & More:

Microorganisms of all types can grow in a poorly treated spa. Sanitizing is the only thing that keeps spa water clean, healthy, enjoyable and from becoming old bath water. Microorganisms including algae, bacteria, slimes and mold can present themselves in various ways: cloudy water, slimy growths or slippery underwater surfaces. The warm temperature of the spa or hot tub can accelerate the growth of microorganisms. Today, there are many more choices of spa water sanitizers: chlorine, bromine, biguanide, ozone ultraviolet, mineral purifiers and ionization. Using a combination of two – one as the primary and another as a backup – produces consistently good results and sparkling clear spa water. Proper spa water treatment has never been easier or more convenient.


Spa Foaming:

Foaming and scum formation are serious detractions from the goal of crystal clear spa and hot tub water. Spa chemicals generally do not cause foaming, although biguanide can cause some low level foaming. The most common cause is the reaction of body oils and cosmetic residues with the natural alkalinity of the water. This can lead to the formation of “soaps” and the possibility of a foamy water problem. While anti-foam can help, the problem may recur. Foaming spa water can be controlled and eliminated with the use of Enzyme Products and avoiding “soft” water conditions.


Slime & Odor:

Slimes are films of microorganisms, usually bacteria or algae that can be found on the underwater surfaces of inadequately sanitized spas and hot tubs. Biofilm is another common phrase. That slippery, slimy feeling on underwater spa surfaces, especially those in hard to reach spots, is evidence of this problem. Proper sanitation and circulation of the water will eliminate and prevent this problem. Microorganisms can be associated with the development of spa water odor problems. However, odors can result from chemical conditions, especially very low pH and high levels of chlorine and/or bromine.


Rashes & Irritation:

Rashes and irritations in spas or hot tubs occur for two principal reasons: bacterial infections or chemical dermatitis. It is recommended that persons exhibiting these problems seek a medical opinion. Bacterial infections can be the direct result of inadequate sanitation. Chemical dermatitis can be the result of excessively high levels of chemical agents and/or extremes in pH or the presence of irritating, unwanted byproducts. Some individuals seem to be more sensitive, to even normal levels of common sanitizers, and may be helped by a switch to an alternative sanitizing method.

Spa Water Sanitizers


Chlorine is used as a spa or hot tub sanitizer, typically in the form of granular sodium dichlor. The other forms of chlorine, popular in pools, are not used in spas and hot tubs for a variety of seasons: solubility, build-up considerations and effect on the pH. Chlorine can be used as a backup sanitizer or oxidizer, in conjunction with Ozonation or Ionization.


Chlorine Generator, Salt:

Salt Chlorine Generators, also referred to as Salt Chlorinators, Saltwater Chlorinators or Salt Chlorination Systems, are actually miniaturized chlorine manufacturing plants: the same technology is utilized. The devices are plumbed in-line and work by electrolytically converting salt, in the spa or hot tub water, into chlorine as it passes over specially coated titanium electrode plates. Salt must be added to the water prior to start up, as directed. Thereafter, salt need only be added occasionally, to replace that lost due to splash out, pump outs or back washing. The device generates Free Chlorine and destroys odorous and irritating chloramines, as the water passes through the cell. Chlorine production is regulated by a controller setting and the equipment operates in conjunction with the timer controlling the filter. Properly used, there is much less sensation of chlorine being present. The other water analysis parameters must be maintained, as with any chlorine-maintained spa or hot tub. It certainly is easy-to-use and convenient and lends itself to automation.



Bromine is much more popular in spas and hot tubs, than in swimming pools. For use in spas and hot tubs, it is available in two forms: slow-dissolving tablets or a quick-dissolving 2-part system. Bromine, in functioning as a sanitizer, produces less odor than chlorine and tends to be less irritating. The use of bromine is popular as a backup sanitizer or oxidizer for Ozonation, Mineral Purifiers or Ionization.



Biguanide (PHMB) is the generic name of one of the more popular non-chlorine, non-bromine chemical sanitizers. The main advantage is that no chlorine or bromine is required and there is little chemical odor. Biguanide is an effective bactericide and can replace chlorine or bromine in that function. However, chlorine or bromine are also oxidizing agents that can destroy organic contamination: biguanide cannot destroy organic contamination and, therefore, concentrated hydrogen peroxide must be added to the spa or hot tub on a regular basis. A disadvantage of biguanide is the development of biguanide-resistant micro-organisms, after several years of product usage. This usually takes the form of a pink slime or water mold.


Ionizers & Mineral Purifiers:

Ionizers and Mineral Purifiers are devices that supply a stream of copper, silver or zinc ions to the spa or hot tub water. The copper ions function as an algaecide and the silver or zinc ions function as a bactericide. Used properly, the ions are maintained at very low levels, avoiding the possibility of staining or discoloration. Ionization units use metallic electrodes and electrical circuits to release the ions into the water. Mineral Purifiers accomplish a similar release, without the use of electrical components. Ionizers and Mineral Purifiers are not stand alone water treatment products, but can reduce the total amount of chemicals required for proper spa or hot tub water maintenance. Copper, silver and zinc ions will not destroy organic buildup and contamination and will not oxidize dead microorganisms and organic debris. This requires spa water oxidation and the use of agents such as: chlorine, bromine, non-chlorine shock or ozone. Not all of these oxidizers can be used with all Ionizers and Mineral Purifiers: check with the manufacturer before adding chemicals, as to any limitations that might be suggested.



Ozone (O3) is a form of oxygen (O2) and is a powerful oxidizing agent that can help control microorganisms, destroy organic contamination, build up byproducts, dead algae and organic debris. It is not a complete spa or hot tub sanitizer, in the truest sense, because ozone does not remain in water for long periods of time. There must be a backup sanitizer such as: chlorine, bromine or ionization. An Ozone Purification System will reduce the quantity of the backup sanitizer required for proper sanitation. The devices that generate Ozone fall into two categories: UV or Corona discharge. Commercial spas and other high bather usage installations should utilize a corona-discharge type of unit, as it is capable of producing the greater quantities of ozone that these situations require. With ozonation, the water should be maintained in the typical manner.


Ultra-Violet (UV) Sanitizers:

Ultra-Viole t (UV) light can be used as an alternative sanitizing method to very effectively destroy microorganisms in spa or hot tub water. Up to 99.9% of the microorganisms can be destroyed, as the water passes through the UV unit. This dramatic reduction, in the microbial populations, helps to better maintain proper, sanitary spa water conditions: reducing the amount of chemical sanitizer needed to maintain water quality and to keep the underwater surfaces free of bacteria and slimy deposits. Typically, an Ultraviolet Sanitizer is plumbed inline and operates with the filter pump cycle. Water passing through the cell is efficiently sanitized, as the ultraviolet light passes through the microorganism’s cell membrane.


Shock Treatment:

Shocking a spa or hot tub refers to the application of large quantities of chlorine, non-chlorine shock or hydrogen peroxide. Typically 5-10 times the normal dose is used, based upon actual conditions and needs. The purpose of this large dose is to break down the combined chlorine, organic waste and contamination and re-establish a positive level of sanitizer. Shock treatments must be repeated, until such time as a stable sanitizer reading can be achieved, for at least a few hours. Products such as sodium dichlor and non-chlorine shock are used for this purpose, with spas utilizing chlorine, bromine, ozonation, ultraviolet treatment, mineral purifiers or ionization. These products cannot be used in a biguanide-maintained spa: only concentrated hydrogen peroxide can be used as the shock. A spa should be shocked at the first signs of algae or slime, after periods of heavy bather usage and at the onset of a loss of water clarity or quality. Another common practice is to shock treat the spa water every week, typically, after a period of high bather usage. This will help to re-establish the sanitizer level, help prevent the growth of resistant microorganisms and help maintain sparkling, crystal clear spa water.

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