Commonly known as "Pool Sunscreen" or "UV Blockout", here we dive into the nitty grittys of Cyanuric Acid.

A common pool service household name, cyanuric acid is now in the toolbox of most residential and commercial pool service professionals who are servicing outdoor pools.

Where did it come from?

Since its invention in 1829, it has been revered as invaluable and essential to keeping chlorinated pools clean and sanitary. At the same time it is labelled as misused, controversial and dangerous. To illustrate this contradiction, some health inspectors insist on the use of cyanuric acid and some health inspectors restrict its presence in public pools. How can this be the case among so many experts? Let’s take a deeper dive into the benefits and misconceptions of cyanuric acid.

Cyanuric acid, as its name suggests, is an ‘acid’. Like many commercially available acids, it is sold as a white crystalline powder, is able to easily dissolve in water and has little overall effect on other pool chemicals, such as pH, alkalinity and dissolved solids. Unlike other ‘acids’, it is commonly referred to as a chlorine stabiliser or conditioner, forming a weak and temporary chemical bond with chlorine. This means it will chemically hold onto free chlorine in the water, slow down overall oxidation reaction rates and most importantly, protect chlorine from the sun’s UV rays until the chlorine is consumed for oxidation or disinfection of material in the pool. If you are needing to test for cyanuric acid use our 7-in-one test strips.

The primary benefit of cyanuric acid in pools

A chlorinated pool with cyanuric acid will remain chlorinated in direct sunlight; whereas without a stabiliser, chlorine will dissipate and leave the pool unprotected without free chlorine in a matter of hours. Most importantly, cyanuric acid will not be consumed in this helpful work and will, over time, start to build up in pool water. Cyanuric acid has many extraordinary benefits for the pool industry. It has allowed the typical homeowner to manage a pool’s water chemistry with less effort and with higher consistency. Allowing for weekly water maintenance instead of daily has created an opportunity for service companies to take care of more pools with less hassle and fewer emergency house calls (algae, etc). Overall, the market for cyanuric has exploded, creating a US$300 million a year business. Unfortunately, the misconception of ‘if some is good, more is better’ has perpetuated throughout the industry and could not be further from the truth.

Consequences of high cyanuric acid levels

Chlorine’s potential to oxidise, often measured as oxidation-reduction potential (commonly referred to as ORP), is a good indicator of the effectiveness of chlorine to oxidise and sanitise swimming pool water. Over the years, numerous independent and academic research initiatives have shown when cyanuric levels build up in the pool, ORP levels consistently drop, indicating that the effectiveness of chlorine diminishes. In addition, there is a clear correlation to increased levels of cyanuric acid and the time it takes to effectively kill bacteria present in pool water. The chart below demonstrates the amount of time to kill 99% of bacteria at various levels of cyanuric acid and different levels of chlorine.

What happens when your cyanuric acid level is too high? It is simple — the only reliable method to remove cyanuric acid from swimming pools is through draining/dilution or removal through reverse osmosis.