Spa Maintenance

One of the most popular attractions in a public or private aquatic facility or health club is the spa, hot tub or whirlpool bath which features hot, swirling, water that provides a sense of relaxation, health and well being.

But this popular attraction has become a major health concern for most facilities because of increased risk of bacterial infection resulting in the common Pseudomonas Aeruginosa, which creates an uncomfortable skin rash or the more serious Legionella Pneumophila (Legionnaire's disease) which has been evident on a cruise ship and in some display and backyard spas.

Dr. R. Neil Lowry, a Ph.D in inorganic chemistry, is a consultant to the swimming pool and spa industry and a regular contributor to this publication. He has written several articles on hot water maintenance and stresses the importance of using the proper sanitizers for the unique conditions of spa water, maintaining adequate levels of sanitizers and chemical parameters for spa water, and most importantly, the regular dumping of spa water to insure cleanliness.

This article is a synopsis of several articles produced by Dr. Lowry and should be an easy guideline to the proper maintenance of any hot water installation.

Sanitizing Chemicals

There are a number of products on the market that will sanitize water. However, the high temperature and small volume of spa water makes hot water unique in the required treatment. These two areas of distinction differentiate spa water from pool water.

A. High Temperatures

• Greater tendency for scale formation

• High TDS (Totally Dissolved Solids) as higher evaporation rat

• Higher levels of organics from bather

• Faster chemistry

• Pseudomonas growth

B. Small Volumes

• High turnover rate of spa water

• Chemical dosage sensitivity

• Heavy bather load

• Low total reserve of sanitizer

Constant feed of the sanitizer and oxidizer is extremely important to the cleanliness of spa water.

In hot water, the chemical reaction proceeds twice as fast for every 10 degrees C that the water is raised. Spa maintenance staff may notice that chlorine levels are constantly being depleted and may think that the hot water is decomposing the chlorine. However, chlorine residuals are quite stable in clean, hot water which creates no chlorine demand. The combination of a higher reaction rate in the hot water and the created chlorine demand, caused by the moving, hot water drawing more organic materials from the body, creates the conditions that use up the chlorine at a faster rate, therefore, maintaining chlorine levels through constant feed, to meet the increased demand, is essential.

There are three products that best suit the spa market for sanitation. In the chlorine lines there are two products, Lithium Hypochlorite (a granular chlorine that contains no calcium) and Sodium Dichloro-s-triazinetrione (a fast dissolving stabilized chlorine granule) that has the unique property of being pH neutral. It should be noted that any chlorine sanitizer has the drawback of forming combined chlorine or chloramines. Formed by the combination of chlorine and ammonia based chemicals from bathers, chloramines have the characteristic pungent chlorine odor coming from heavily used spas. Besides the disagreeable odor, they are irritants to the eyes and mucous membranes of bathers. Combined chlorines also are too slow a sanitizer to be effective in spa waters.

Slow dissolving Bromine tablets are analogous to chlorine sanitation and have certain defined advantages when used for spa water sanitation. First, bromamines have little odor or bather irritation and are good sanitizers themselves.

Second, bromine residuals are more effective than chlorine over the broad range of pH values experienced in the small volumes of spa water. Being slow dissolving, bromine tablets lend themselves to a constant feed system. The one negative aspect of brominating tablets is that they are an acid feed sanitizer with a pH of 4.8 which can quickly deplete total alkalinity and lower pH.

A second type of bromine utilized in spas is a two part sanitizer system. This is based on the fact that when bromine is reduced during sanitation and oxidation, it is converted to a "bromide bank" which is a concentrated level of bromide ion. This "bank" can be oxidized by chlorine, ozone or potassium monopersulfate back to the "active" bromine residual.

Suggested Ranges

Compared to pool parameter values, there are some significant differences in the levels of spa water parameters. Lower levels of calcium hardness and pH compensate for the scale formation tendency of hot water. Sanitizer levels are significantly higher than pools due to the lack of total sanitizer reserve due to the higher chlorine demand. Stabilizer levels of 100 ppm are required for most states and provinces with the exception of Ontario which requires only 60 ppm.

Suggested Ranges For Spa Water Chemical Parameters

Total Alkalinity 80-120 ppm
Calcium Hardness 150-200 ppm
pH 7.2-7.6
Chlorine/Bromine 5.0-10.0 ppm
Stabilizer 100 ppm (max)

It is also recommended that after each period of use, the level of the sanitizer should be raised to its maximum of 10.0 ppm. This is to avoid having heavily loaded spa water sitting for periods of time with a zero sanitizer level. If the water is murky, or if the sanitizer level is difficult to attain, additional superchlorination may be required.

Drain The Water

Periodic complete draining of spa water is the most important component of proper spa water maintenance. High bather loads and the hot water conditions cannot be handled over long periods of time without draining the spa. The following is a dumping formula that is in the guideline: "Recommended Standards for the Operation of Public Spas," by the Ministry of Health, Ontario and should be followed.

Number of Days Between Draining Spa = 1/ 3 (volume in US gals) / Maximum Number of Daily Bathers

or in metric measurement

Number of Days Between Draining Spa = Spa volume in liters / 10 x Maximum Number of Daily Bathers

Example: If you have 100 people using a 600 gallon spa in a day, the spa should be dumped every 1 / 3(600) / 100 = 2 days. If this procedure isn't followed, the spa will become quite unsanitary very shortly.

A key indicator of a spa out of control is the formation of residual foam when the spa pump is turned off. This is unsanitary as the surface of the bubbles harbors bacteria which floats on the sanitized spa water. This bacteria is not destroyed and serves as a constant source of bacteria inoculation into the spa water. Foam formation will not occur if the draining formula is obeyed.

In summary, spa water chemistry differs from pool water chemistry because of extreme bather loads, propensity for scale formation and a small total reserve of sanitizer in the hot water. The key to safe water is the constant feed of a good sanitizer, proper chemical ranges, and, most important, the periodic, complete draining of spa water and the refill with fresh water. In this way you will maintain a healthy, properly sanitized body of water.

Article derived from Pool & Spa Marketing, April 1998