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In hot water: if you're treating your spa water the same as your pool, you re asking for trouble.

When it comes to aquatic venues, spas have gotten a bad name. In fact, more than half of them--57 percent to be exact--may be unsafe, according to the Centers for Disease Control, which inspected more than 5,000 spas across the country in 2004. The biggest violation? Poor water quality.

Clearly, the industry needs to do better.

A good place to start is to understand one basic tenet: Pool and spa water must be cared for in different ways. Spas operate at higher temperatures, and they are much smaller. These two facts change everything. That is why the Association of Pool & Spa Professionals has established separate standards for spas and pools.

The two big differences-higher temperature and smaller volume--cause a number of other differences that need to be taken into consideration.

In general, pools operate between 76 to 86 degrees (25 to 30 degrees Celsius), while spas fall in a range of 96 to 104 degrees (36 to 40 degrees Celsius). This difference in temperature changes the water chemistry in important ways.

Chemical reactions rake place much faster in spas than in pools. For every 18 degree (10 degrees Celsius) increase, the chemical reactions proceed twice as fast. For instance, a spa at 102 degrees allows chemical reactions to happen in half the time of a pool at 84 degrees. Any chemical adjustments occur more quickly as well. The water comes to equilibrium sooner, and water treatment can be completed in a shorter period of time.

The water in a spa also evaporates at a high rate due to high water temperature, rapid water circulation and aeration. As the water evaporates, spa operators must add makeup (fill) water to refresh the system. Any water that evaporates is pure; basically pure water leaves behind everything else--the stuff that we call total dissolved solids or TDS. Makeup water also contains minerals, salts and other things that increase the total dissolved solids, so adding fresh water is increasing the TDS level as well. High levels of TDS decrease the effectiveness of some chemicals and may cause cloudy water.

Higher temperatures in spa water will cause most chemicals to dissolve faster than in lower temperatures, except calcium carbonate. This form of hardness works in the opposite way: It is actually more insoluble in hot water. Therefore, calcium carbonate scale is more likely to occur in hot spa water.

The hot water in spas also makes people sweat. The average bather sweats a pint (approximately half a liter) in just 20 minutes. Plus, the power jets in a spa can scrub off dirt and dead skin very quickly. All this means that the filter and chemical sanitizer in a spa have to process a high percentage of waste. Consequently, paying close attention to the sanitizer level is critical.

Without that care, a spa makes a perfect incubator for bacteria. Hot water promotes the growth of most types of bacteria. Susceptible bathers can acquire serious illnesses if water is chemically imbalanced.

In addition to their temperature differences, spas have a much smaller volume of water than pools. This glaringly obvious difference leads to some other differences that may not be as obvious.

Spas experience a much heavier bather load because they are so much smaller. While two people in a spa might feel cozy, being in a pool where the swimmers are elbow to elbow is not. A common load in a spa would have one person in 100 to 400 gallons of water. Pools tend to have at least 10 times that amount of water for every swimmer. Consider this: Two bathers in a 400-gallon spa are roughly equivalent to 150 people in a 30,000-gallon pool.

This significant bather load can decrease the sanitizer levels quickly. As a result, many places set regulatory limits on the number of bathers allowed in a spa at the same time. A common standard for public spas is one person per one square meter of surface area.

Because of the lower water volume in a spa, chemicals need to be measured precisely and the water tested more often. Misjudging the required dosage can drastically alter the chemistry in such a small amount of water. For this reason, there are chemicals specifically designed and labeled for treating spas. These lower the risk of adding too much or not enough of a particular chemical.

The water in a spa should turn over every 25 to 45 minutes when the system is running with the proper filtration, due to the smaller volume and increased wastes. The water in a pool might turn over in six to 12 hours. The faster turnover rate can take a toll on the spa's filtration system, particularly if the chemicals are not in proper balance. As a result maintenance on the filter will need to be performed more frequently.

A spa, with its small water volume and higher water temperature, uses up the sanitizer residual very quickly. This is why you need to maintain a higher level of sanitizer in spa water than you do in your pool. The APSP standards reflect this fact, requiring sanitizer levels to be higher in spas.

Finally, the spa's water volume means that even small additions of sanitizer and other chemicals can have an immediate effect on the pH of the water. If the wrong amount of a chemical is added to a pool, there is a little time before the chemical circulates throughout the entire system. In the case of a spa, that reaction time is lost. To avoid equipment damage, the sanitizer should be measured carefully and the pH tested frequently.

Treating a spa the same way you treat a pool will not work. Because of the higher temperatures and smaller volumes, a new set of rules comes into play. Understand the unique features of spa water chemistry to ensure bather safety and lower the risk of harming expensive equipment.

Spa Dynamics

Effects of Higher Temperatures

* Faster chemical reactions

* Faster evaporation rate

* Increased scale formation

* More organic waste in the water

* Accelerated bacteria growth

Effects of Smaller Water Volume

* Heavier bather load

* Exact chemical dosages needed

* Higher filtration (turnover) rate

* Faster depletion of sanitizer residual

* More abrupt changes in pH

Joe Sweazy, Environmental Test Systems
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Title Annotation:polluted water
Author:Sweazy, Joe
Publication:Aquatics International
Geographic Code:1USA
Date:Nov 1, 2005
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