Spas: Hot Water Basics
By Terry Arko
In fact a spa is much more than just a tiny swimming pool. There are many differences between a pool and spa, and these differences call for a different and more strategic plan for care:
- Most pools have a maximum temperature of 80 degrees; for spas it's 92 to 104 degrees.
- A higher evaporation rate leads to more scale and increased calcium levels.
- Air jets and blowers cause quicker chemical reduction.
- The smaller body of water means a greater affect on pH, total alkalinity, calcium hardness and TDS from added chemicals.
- The bather load ratio is far different.
Balanced water is critical in a spa. There are two main adjustments to be made when dealing with spa water:
Total Alkalinity: This creates a buffer in your water so that it can resist any acids that may be added to the water. This is the first and most important adjustment to be made. Total alkalinity acts as a control to the pH. The pH cannot be properly adjusted if the total alkalinity is out of the suggested ranges. The recommended total alkalinity range in spas is 80 to 120 ppm.
pH: This is a measurement of the acids or bases in the water. A low pH indicates the water is primarily acidic. A high pH means that the water is more base or alkaline.
A good tool for adjusting and holding pH and alkalinity in place between drainings is to use a product that holds the pH steady by boosting the total alkalinity. The technology raises the alkalinity by adding a soft form of calcium to the water. The result is the pH gets locked in and can't be easily affected by acids.
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.
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.
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