The sun’s ultraviolet (UV) rays will make the chlorine in anoutdoor pool dissipate quickly. In fact, an ideal level of chlorine in an “unstabilized” pool or spa can be lost in less than two hours on a bright sunny day, due to the UV rays of the sun. Cyanuric acid acts as a “stabilizer” that helps chlorine hold up better when exposed to the UV rays. You can think of cyanuric acid as blocking the effect that the sunlight has on breaking down the chlorine—kind of like a sunscreen for your pool.

You should maintain an ideal level of cyanuric acid, 30 to 60 ppm (mg/L), to prevent rapid chlorine loss. If the cyanuric acid level is too low, you may need to add more to the water. However, be advised that cyanuric acid will make the pH of the water lower (more acidic), so you may have to adjust the pH upward as well.

On the other hand, too much cyanuric acid will reduce the beneficial effect of your chlorine, leading to stains or cloudy water. Some chlorine compounds already contain an amount of cyanuric acid. If you are using dichlor or trichlor as your primary chlorine sanitizer, you are already introducing cyanuric acid along with the chlorine.

  • For every 10 ppm Free Chlorine (FC) added by Trichlor, it will also increase Cyanuric Acid (CYA) by 6 ppm.
  • For every 10 ppm FC added by Dichlor, it will also increase CYA by 9 ppm.

If the cyanuric acid level in your pool or spa is too high, you will need to drain and refill with fresh water. There is no chemical means of lowering Cyanuric Acid.