A Pool Chemical With Many Names
by John A. Garvin, CSP
Cyanuric Acid, Isocyanuric Acid, Chlorine Stabilizer, Conditioner, CYA...
...whatever you call it, it MUST be understood!
In 1958 it was discovered that Cyanuric Acid would inhibit the loss of chlorine due to the effects of the ultraviolet rays of the sun in swimming pool water . When it is dissolved in water at 25 parts per million, chlorine residuals last three to five times longer than water without Cyanuric Acid. Therefore, using Cyanuric Acid as a chlorine stabilizer meant that you were able to maintain chlorine residuals more easily and economically.
This fact revolutionized the pool service industry and the use of Cyanuric Acid has grown into a $400,000,000 a year industry and is so profitable the motivation to continue promoting it's use is intense, to spite it's negative aspects.
The ideal and most efficient range to maintain cyanuric acid is 20 to 40 parts per million and at this level the optimum protection from ultraviolet radiation is accomplished. Levels maintained above 40 part per million were found to provide no additional advantage in chlorine protection.
The Florida Health Department pool code requires pool operators to maintain Cyanuric Acid levels in swimming pools below 100 parts per million. In commercial spas, with temperatures of 104 degrees F and heavier patron use relative to the water volume, the level must be below 40 parts per million. In fact, concerns about difficult water sanitation in heated spas has recently prompted the Health Department to prohibit the use of chlorine tablets (tri-chloro-s-triazine-trione) in spas, thereby eliminating the Cyanuric Acid by-product altogether. Their rationale is that at higher levels there is a carcinogenic (cancer) hazard that needs to be avoided.
While Cyanuric Acid has the afore mentioned benefits, there are also some undesirable features to it's use. In addition to the carcinogenic hazard mentioned above, there is also a significant problem with
"over stabilization" that causes the chlorine to become less effective as cyanuric levels rise. In fact, at high levels of 100 parts per million and above, in addition to the violation of health department code, a dynamic process referred to as "chlorine lock" is created. This condition causes cloudiness and increased algae growth, especially diatom algae. Furthermore, recent studies are now showing that high concentrations of cyanuric acid may be the cause of spot etching and/or other plaster degradation issues. Cyanuric acid can only be lowered from the pool water by draining, splash-out, back washing the filter to waste or dilution from rain.
Cyanuric Acid is an unavoidable by-product that remains in the water when chlorine tabs (tri-chloro-s-triazine-trione) are used as a sanitizer source and therein lies the problem. The measured level of Cyanuric Acid will continue to increase to undesirable levels until; the tablets have been substituted with an un-stabilized product, draining and refilling all or a portion of the pool water, or dilution from torrential rains.
There is another serious problem resulting from high Cyanuric Acid levels. That is that 30% of the Cyanuric Acid present in the water is measured as alkalinity but has no value as a pH buffer, and this skews the results of the "Total Alkalinity" test. When water contains over 100 parts per million of Cyanuric Acid, the error is so significant that a correction must be deducted from the measured "Total Alkalinity" in efforts to achieve correct water balance. Overlooking this necessary correction risks having corrosive and out-of-balance pool water that damages the equipment and the pool surface. To better understand this problem, refer to the PDF document entitled "The Correct Approach".
We therefore suggest using unstabilized "Sodium Hypochlorite (liquid chlorine)" which contains no Cyanuric Acid. The only problem is that the Cyanuric Acid level tends to deplete over time due to splash-out, back-washing the filter to waste or dilution from rain. Therefore, the cyanuric acid level needs to be monitored in a timely fashion maintained at the beneficial level of 20 to 30 parts per million. You simply run the Cyanuric Acid test and add small amounts of granulated Cyanuric Acid to the pool water.
It should be obvious from what you read above that the control of pool water balance and Cyanuric Acid levels can be best accomplished by using liquid chlorine as a sanitizer or a Watermaid System which manufactures Sodium Hypochlorite in your swimming pool from common Sea Salt or an Automatic Dosing system for commercial pools.
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The above article points out the reasons why Watermaid Europe, S.L. recommends residential pools be equipped with a WATERMAID saltwater chlorination system and the installation of Automatic Chlorine dosing systems for Communual and Commercial Pools
IDEAL CYANURIC ACID LEVELS
The chart below (figure 1) shows the "staying power" of chlorine in swimming pool water at different cyanuric acid levels. The percentages represent the amount of chlorine remaining in pool water after one hour. It is easy to see that any level beyond 40 parts per million has very little additional benefit. Not only are excessively high levels of cyanuric acid economically unwise, but levels in excess of 70 ppm begin to cause "chlorine lock" making algae growth more prevalant
Swimming pools that are sanitized using slow dissolving, 'stabilized' tabs run the risk of exceeding these levels. This is because the binding agent used in this product is cyanuric acid. Watermaid Europe, S.L. discourages the use of these 'stabilized' products. . To obtain the correct stabilizer levels, cyanuric acid is hand fed when needed to achieve the optimum 20 to 40 parts per million. On residential swimming pools, we use the Watermaid Saltwater Chlorination system and on communual and commercial facilities an Automatic dosing system to feed sodium hypochlorite as the sanitizing agent.
More information on 'overstabilization' can be found at archchemicals.com, the leading manufacturers of stabilized chlorine.
Fig 1
The chart below (fig 2) shows the amount of cranuric acid that needs to be added to achieve 50 part per million. The chart is based on the current stabilizer reading in ppm.
AMOUNT OF CYANURIC ACID REQUIRED TO OBTAIN 40 PPM
CURRENT SIZE OF POOL IN GALLONS
READING 15,000 20,000 25,000 30,000 35,000 40,000 45,000 50,000
0 PPM 4.8 lb 6.4 lb 8.0 lb 9.6 lb 11.2 lb 12.8 lb 14.4 lb 16.0 lb
10 PPM 3.6 lb 4.8 lb 6.0 lb 7.2 lb 8.4 lb 9.6 lb 10.8 lb 12.0 lb
20 PPM 2.4 lb 3.2 lb 4.0 lb 4.8 lb 5.6 lb 6.4 lb 7.2 lb 8.0 lb
30 PPM 1.2 lb 1.6 lb 2.0 lb 2.4 lb 2.8 lb 3.2 lb 3.6 lb 4.0 lb
Fig 2
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High Cyanuric Acid Levels & Plaster Degradation In Swimming Pools
by Ellen M. Meyer, Ph.D
Ellen M. Meyer, Ph.D., is technology manager of Arch Water Products in Smyrna, Georgia, a leading global supplier of swimming pool and spa sanitizers and related products.
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It is well known that the build-up of cyanuric acid stabilizer in swimming pool water will cause
overstabilization, which usually results from the extended use of stabilized sanitizers in conjunction
with stabilized shock treatments.
It is also known that overstabilization decreases the effectiveness of chlorine in killing bacteria and
algae and will reduce the oxidation reduction potential or the oxidizing power of chlorine.
Low levels of cyanuric acid do serve a purpose in protecting chlorine from sunlight degradation,
however, too much cyanuric acid will negate any benefit and cause problems.
When used properly, the recommended level of cyanuric acid is between 20 and 50 parts per
million (ppm). Cyanuric acid use is not recommended for indoor pools.
To determine the effect of cyanuric acid on sections of white pool plaster, Arch Chemicals
conducted laboratory studies in 2004. The levels of cyanuric acid tested were 200 ppm and
500 ppm. After five weeks, the cyanuric acid in the water with the plaster 'coupons' - which are
individual rectangles of plaster made using the same plaster composition that is used for pools - had dropped considerably and surface analysis showed the accumulation of cyanuric acid on the plaster. Surface reaction was observed at 250 ppm and 500 ppm, with the reaction of cyanuric acid being much faster in the 500 ppm sample, as shown in the graph entitled 'Cyanuric Acid Reacts with Plaster'.
Based on these initial results, a six month tank test was conducted to better understand the effect of cyanuric acid on plaster. The water in the tank tests was was adjusted to try and maintain pH between 7.2 and 7.8 and alkalinity between 60 ppm to 100 ppm. Because the plaster coupons were new, the pH rose continuously and therefore needed to be adjusted daily. The free available chlorine was maintained between 1 ppm and 4 ppm and cyanuric acid levels of 0 ppm, 25 ppm, 50 ppm, 100 ppm, 250 ppm, and 500 ppm were tested. Images taken with a scanning electron microscope at a magnification level of 250X show degradation of the plaster surface at increasing levels of cyanuric acid (see photo at bottom of page).
There was little plaster degradation at 100 ppm cyanuric acid. Due to the results of the tank tests, additional tests were initiated in larger bodies of water where the water balance parameters could be maintained more easily.
Pool testing with plaster coupons was started in May, 2005, with the pools being operated at cyanuric acid levels of 0 ppm - 50 ppm - 110 ppm - 125 ppm, and 200 ppm - 250 ppm. The water parameters were maintained at a pH of 7.2 - 7.6, alkalinity at 80 ppm - 120 ppm, calcium hardness at 180 ppm - 250 ppm, and available chlorine at 1 ppm - 4 ppm.
After four months of operation, photographs show surfave degradation on the plaster coupons in high, 200 ppm - 250 ppm cyanuric acid pools (see photos above).
Results reported in a July, 2004 study conducted by the National Pool Industry Research Center (NPIRC) and the National Plasterer's Council (NPC) indicate that low pH trichlor products can affect plaster surfaces. However, in the NPIRC study, it was difficult to discern whether the effect on the plaster was a result of the low pH or the trichlor sanitizer, or from some other chemical factor.
In the tank studies described above, the pH and alkalinity of the tanks ran on the high side (pH~8, TA~90 ppm), while the pool were being maintained as indicated above. Despite the high pH and alkalinity in the tank test, plaster degradation was still seen. The pool tests further confirmed the effect of cyanuric acid on plaster.
These results indicate that the presence of cyanuric acid can affect plaster surfaces and that a minimum amount should be used only if chlorine stabalization is necessary.
Left: 14X magnification of plaster coupon in pool with 0 ppm cyanuric acid.
Right: 14X magnification of plaster coupon in pool with 200-250 ppm cyanuric acid.
Reprinted from "Pool and Spa Marketing" January - Atlantic City Show Issue - 2006
