Testing for cyanuric acid is often overlooked because it doesn’t seem as critical as other water parameters such as chlorine, pH, total alkalinity and calcium hardness. However, it is important to test for cyanuric acid for several reasons. For one thing, cyanuric acid affects the total alkalinity test, discussed in further detail in an accompanying article. For another, low cyanuric acid is not as effective at protecting chlorine from ultra violet rays. Finally, high levels of cyanuric acid reduces chlorine’s efficiency at oxidizing and sanitizing. It is recommended to keep cyanuric acid concentrations between 30 and 50 ppm, with a maximum of 90 ppm.
In general, there are two ways to test for cyanuric acid.
One test uses test strips in which a chemical reaction takes place between cyanuric acid and a chemical on the test pad. It is a colored reaction where the color change is proportional to the cyanuric acid concentration. The color of the test pad is then compared to a color chart to analyze the cyanuric acid present.
The most common test is a turbidity test, also sometimes called the disappearing dot test. This is typically accomplished using a melamine reagent that, when combined with cyanuric acid, forms a cloudy precipitate. When this cloudy solution is added to a comparator with a mark (usually a dot) on the bottom, the disappearance of the dot signifies the end of the test. The amount of cloudy water needed to obscure the dot corresponds to a cyanuric acid concentration. To perform the test:
• Rinse and fill the CYA dispensing bottle to the appropriate level with sample water.
• Add the reagent to the appropriate level. Cap and mix well.
• Slowly transfer the cloudy solution to the comparator tube, viewing from the top.
• Stop when the black dot disappears.
• Check the liquid level on the back of the comparator block. The reading indicates parts per million CYA.
The test for cyanuric acid is notoriously inaccurate. It is prone to both time dependance as well as interference, and can be influenced by lighting conditions. Common interference includes water temperature and pH.
Check the water temperature prior to running a cyanuric acid test and allow the sample to warm to the ideal temperature of 75 °F before trusting the results. Water temperature that is higher than about 90°F can result in readings that are as much as 15 ppm low. Meanwhile, when the water temperature is below about 60 °F, it can result in readings that are 15 ppm too high.
Also, check the pH and ensure that it has been adjusted to the ideal range of between 7.4 to 7.6 before trusting the results.
If the result is near the endpoint of the test kit, it should be diluted and run again.
For CYA levels at or above the endpoint (generally 100 ppm), do a dilution to obtain a more accurate reading. In a container, mix one part sample water with one part CYA-free water (tap or bottled water will do). Retest and multiply the result by 2. If the result is still too high, do another dilution, this time using one part sample water to two parts CYA-free water, and multiply the result by 3. For a 1:4 dilution, the multiplier is 5. Once the reading is within the scale, you are finished.
