The Affect of UV Rays on your Pool's Chlorine

In outside pools the sun has a big affect on the chlorine via its ultraviolet (UV) rays. The rays actually cause the chlorine to dissipate. Without stabilizer a perfect level of chlorine in a pool or spa can be lost in less than two hours on a bright sunny day, solely from the sun’s UV rays.

Shades for your Pool
The solution to prolonging chlorine life when exposed to UV rays is the introduction of a chemical called Cyanuric acid. Cyanuric acid acts as a “stabilizer” that helps shield the chlorine to the dissipating affects of the UV rays. Some have called it a “sun block” or “sunglasses” for your pool.

Minimum Cyanuric Needed
Cyanuric acid must be at least 30ppm chemically to effectively shield the chlorine from UV rays. Due to variances in testers and our desire to avoid being at risk of cyanuric going to low we will usually add cyanuric acid even if the level is 30ppm to get it at least to 40ppm. Our goal is to keep the cyanuric acid above 40ppm at all times.

Too Much Cyanuric?
We allow the cyanuric acid to go as high as 100 ppm (mg/L) before warning customers that it is getting higher than is recommended. While we can on some occasions work with a pool with a cyanuric acid level higher than 100 it makes it harder to get the best results from maintenance. Too much cyanuric acid reduces the effects of chlorine as both an oxidizer and disinfectant meaning more chlorine is required to get the same results. It can also lead to the pool being more at risk of stains and cloudy water. If it gets higher than recommended we suggest a partial drain of the pool water.

Cyanuric Creep
A number of commonly used forms of chlorine have an amount of cyanuric acid already contained in them. Examples include dichlor (typically a granular form) or trichlor (typically tablets). Using either or both of these means a small amount of cyanuric acid is being introduced to the pool water along with the chlorine. When used properly in conjunction with other forms of chlorine these amounts of cyanuric acid being introduced should not put it out of range for a number of seasons. Since it is recommended to do a partial drain of a pool every few seasons anyway the use of dichlor and trichlor should not normally cause any additional maintenance beyond what is already needed every few years via a partial drain.

The Remedy for Too Much Cyanuric 
If the cyanuric acid level is your pool or spa is too high, you will need to partially drain and refill with fresh water.When you first fill your pool or spa, test the cyanuric acid level until you have added enough to reach the ideal range. After that, test cyanuric acid of once a month throughout the pool season.

Affects When Adding Cyanuric Acid
Adding cyanuric acid will lower the pH of the water making it more acidic. When adding it we commonly add sodium bi-carbonate or sodium carbonate to offset the affect on pH.