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.

In this blog, we're going to get into the technical side of things for those who want to know more about how a specific chemical, in this case Cyanuric acid, works so that they'll get a fuller understanding of what goes on in their pool.

Where did Cyanuric Acid 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.

What happens when your cyanuric acid level is too high? It is simple, your chlorine no longer works as it should be — the only reliable method to remove cyanuric acid from swimming pools is through draining/dilution or removal through reverse osmosis, which can be a really expensive endeavour.

UPDATE: There's now a way to reduce your cyanuric acid levels without reverse osmosis or without draining out thousands of liters of water and wasting other chemicals. This is with the use of the Bio-Active Cyanuric Acid Reducer! For more information, check out the product spotlight for the Bio-Active Cyanuric Acid Remover here.


Too much of a good thing can be bad. This is especially true when it comes to cyanuric acid levels in your pool. Remember, it's called "balancing your pool" and not "dumping as many chemicals as you can into your pool" so the best practice is, test your pool often and make sure that the cyanuric acid levels are where they are supposed to be. When adding cyanuric acid, shoot for the lowest amount possible, it's easier to add more than take it out.

When adding chlorine, only use stabilised chlorine when your cyanuric acid levels are very low, when topping up chlorine, use only unstabilized chlorine to prevent your cyanuric acid levels from rendering your chlorine useless.

For more information on pool chemicals, don't forget to check out Mr Pool Man's Ultimate Pool Chemical guide. New Pool owner? Check out this link for more blogs.

Do you have any questions about this topic or the featured products? No worries, we're here to help! Drop us a question down below and we'll get back to you ASAP.

Happy swimming :)

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