Don't Get Burned by the Sun
By Joe Sweazy
Special to Aquatics International
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July/August 2002
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unlight and its ultraviolet radiation can destroy sanitizer in a very short time. The more intense the sun and UV, the quicker the sanitizer degrades. For instance, on a sunny day, nearly all chlorine (the most commonly used sanitizer) in an unstabilized pool can be lost in less than two hours. However, chlorine can be protected from the sun with cyanuric acid (CYA), or Triazine-2, 4,6-Triol.
The ideal level of cyanuric acid to thwart chlorine loss is 30 to 50 ppm. At that level, CYA combines with chlorine to shield it from the UV rays, but releases chlorine on demand when it is needed to sanitize the water. It’s like sunscreen for your chlorine.
CYA is so effective against chlorine’s UV degradation that some chlorine compounds have been developed that already contain cyanuric acid, such as dichlor or trichlor — often known as stabilized chlorine. Usually, no additional cyanuric acid is needed when using a stabilized chlorine compound.
However, because CYA is an acid with a pH of approximately 4.0, it may lower the pH of the water when added directly to a pool. That, in turn, reduces chlorine efficiency and contributes to a high level of total dissolved solids. Under these conditions, it may take chlorine longer to kill bacteria and other microorganisms.
When CYA levels are too high, you must drain and refill the pool with fresh water to lower the level. Local health authorities often require commercial pools to maintain under 100 ppm. On the other hand, low CYA levels (less than 30 ppm) indicate that the chlorine will dissipate very quickly when exposed to sunlight.
Testing CYA
CYA levels should be tested upon the addition of fresh water and then tested a minimum of once a month throughout the season. If dichlor or trichlor are being used, cyanuric acid may need to be tested more frequently to ensure that the level has not exceeded the upper limit. Each time a dose of one of these stabilized chlorine compounds is added, the level of cyanuric acid increases slightly.
Two methods for testing cyanuric acid are commonly used in the pool and spa industry: test strips and turbidity tests.
A recent improvement in the test strip sector allows users to measure up to 300 ppm directly (without the need to dilute a pool water sample). This dip-and-read test is completed in 30 seconds. The turbidity test, often referred to as a “disappearing dot” test, utilizes a chemical reaction that creates turbidity proportional to the concentration of cyanuric acid. The more turbid the water, the higher the concentration of cyanuric acid.
This turbid water is added one drop at a time to a comparator with a mark (usually a dot) on the bottom. A user adds drops until the mark disappears from view. The amount of water in the comparator tube when the mark disappears corresponds to a value marked on the tube to indicate the cyanuric acid level.
The maximum cyanuric acid level that liquid turbidity kits measure is 100 ppm (the point at which the dot disappears). At any level higher than that, it would simply read 100 ppm. The only way a user can determine an actual level above 100 ppm is to dilute and re-test. For example, one can mix a solution of 1 part pool water and 3 parts distilled water. If the liquid test then reads the solution at 60 ppm cyanuric acid, it means the level in the undiluted pool water is 240 ppm (4 x 60).
Once CYA levels are stabilized, you should test routinely to ensure that an ideal CYA level is present.
