Guest Column - April 2008
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Spas: Hot Water Basics

By Terry Arko

Sanitize the water

When it comes to sanitizers there are several choices, although chlorine and bromine are still the two most popular. Chlorine should be maintained at 3 ppm. The best type of chlorine to use for a hot tub is sodium di-chlor. This granular material is available in two different strengths, 56 percent and 62 percent. The pH of both types of di-chlor is near neutral, so it has much less capability of destroying total alkalinity and pulling down the pH.

Bromine should be between 4 and 6 ppm. Bromine can be more practical than chlorine for a service pro. Bromine holds longer in hot water than chlorine, and the service rep can install a bromine feeder to ensure there is proper sanitizing during the week. Bromine generators that use sodium bromide and electrolysis to create sanitizer are another viable option for spas.

UV and ozone units also are available for spas, and can be very helpful to the service pro because they work day in and day out keeping the water oxidized and purified. They are ideal along with a weekly chemical treatment.

Spas also should be shocked with a chlorine-free shock or by using sodium di-chlor granular chlorine at each service.

Using the right chemicals

Many pool pros may fall in to the trap of using the same chemicals in the spas as they do in their pools. This can seem to make sense because they get the products in bulk and save by using fewer chemicals. However, this can also be a very costly mistake. For example tri-chlor tablets are highly acidic and heavily concentrated for treating larger bodies of water. The acidity of tri-chlor tablets will rapidly destroy total alkalinity's buffering capacity leading to severe drop in pH.

Likewise, soda ash should not be used to manage the total alkalinity and pH. This can cause problems and frustration due to the high pH of soda ash being introduced into a small amount of water. It will be particularly difficult to manage the total alkalinity without causing a spike in pH. This pH spike could reach as high as the pH of the soda ash itself, which is 13. Then you play a catch-22, adding acid to lower then adding more soda ash to raise but never being able to reach a balance.

The best way to deal with both total alkalinity and pH adjustment in a hot tub is to use sodium bicarbonate. Sodium bicarb's pH maxes out at 8. So, total alkalinity can be indefinitely raised using sodium bicarb and the pH will go no higher than 8. It is much easier to adjust down from a pH of 8 than a pH of 13.

Another problem is using liquid chlorine to sanitize. There is approximately 1 pound of salt in every gallon of liquid chlorine. When that is being added to a small body of water such as in a hot tub it will cause the total alkalinity, pH and hardness to increase rapidly. Because spas have a high evaporation rate caused by the higher temperature of the water and bather load, the TDS will also spike, which will mean the water will have to be frequently drained. You can also cause scale problems that can lead to plugged filters and equipment failure.


Many service pros only use clarifiers when the water turns cloudy. While clarifiers will work to clear cloudy water, the real purpose of a clarifier is to prevent water from becoming cloudy in the first place. Therefore, clarifiers should be used weekly. It does make a difference what type or clarifier is used. Service pros should make sure to use a natural, non-petroleum-based clarifier. After all, oil in hot water is not a good thing.


Terry Arko has worked in the pool and spa industry for over 25 years. He has worked in service, equipment repair, retail management and chemical manufacturing. Terry is a Certified Pool/Spa Operator. He has spent the last 14 years as a technical consultant specialist in the area of chemical water treatment. He is the author of numerous articles and most recently "The Book on Water Clarity," published by HaloSource Inc. He currently serves as president of the APSP (Association of Pool and Spa Professionals) Region VIII board. He has been called upon to teach water-related seminars at several industry tradeshows. Terry is a products specialist for SeaKlear Pool and Spa Products. For more information, visit