Cyanuric acid is a ultra-violet (UV) blocker used in pools to maintain the power of chlorine, which is destroyed by UV light from the sun. Indoor pools with no direct sunlight do not need additional cyanuric acid.
No Counter to Cyanuric Acid
Although cyanuric acid is important to outdoor pools to keep the chlorine active, it is a cumulative chemical and will eventually exceed the 100ppm level recommended as the maximum. If your pool cyanuric acid level rises significantly above 50ppm you should partially drain the pool. When you refill the pool you will dilute the cyanuric acid and bring the levels down. There is no cyanuric acid in tap water so this is a sure cure.
Where Does Cyanuric Acid Come From?
Whenever you add chlorine to your pool you will also be adding cyanuric acid, even if only in trace quantities. When you do add chlorine to your pool you probably should also add a conditioner or stabilizer. The conditioner or stabilizer will be cyanuric acid.
Because the cyanuric acid is not destroyed or used up it will eventually become too highly concentrated in your pool. When that happens, it will stop protecting the chlorine content and actually stop the chlorine from working. This could lead to stains and the water becoming cloudy which could lead you to make the problem worse by adding more chlorine.
Monitoring Cyanuric Acid
Testing for cyanuric acid should take place once a month but the test strips are rather expensive. In the normal course of pool care and maintenance it takes a couple of years for the cyanuric acid to reach levels of 50ppm but if you use a lot of chlorine tablets or granular chlorine you could be shortening that time.
False Chlorine Readings
If the levels of chlorine you are registering in your pool seem to be too low this could be the result of the cyanuric acid. At levels above 100ppm the cyanuric acid will start to act against the chlorine and effectively neutralize it. Rather than going to the expense of buying a cyanuric acid test kit it is far more sensible to visit your local pool professionals and get them to test your pool water.
Although not always linked, you can sometimes get a hint from the Ph level of your pool that cyanuric acid levels are rising. Too much cyanuric acid will reduce the Ph level of your pool.
Cyanuric acid is necessary in an outdoor pool and the slow build up has no symptoms you could become aware of. When the problems do become obvious it happens quite quickly and the cure is also quick and does not involve any other chemicals to try to achieve or maintain the proper balance.
Testing once a month or even once every two months will enable you to keep the situation under control.