Cyanuric Acid
What is this
Cyanuric Acid, Isocyanurate, and Chlorine Stabiliser are all different names for the same thing. It is a chemical that combines with free chlorine to protect it from UV rays that would otherwise break it down in a short number of hours. This massively reduces the chlorine requirements for your pool and reduces the severity of peaks and troughs in chlorine levels.
What this should be:
Cyanuric Acid levels should be maintained to between 0 - 60 PPM (Parts Per Million) and never higher than 100 PPM.
The ideal level will vary depending on UV (sun) exposure, equipment used and ambient temperature.
UV Exposure
In a pool with little to no UV exposure, such as an indoor pool, cyanuric acid should be avoided.
Temperature
In warmer weather (water temp of 24°C ~ 30°C) cyanuric acid levels should be maintained to 45 - 60 PPM, while colder weather (water temperatures of 10°C ~ 20°C) should result in levels being maintained to about 30 PPM.
ORP Sensor-Based Chlorine Dosing
If an ORP sensor is used, cyanuric acid should be kept to a minimum, preferably under 30 PPM and definitely no higher than 50 PPM. Stabiliser levels should also be kept as steady as possible as spikes or drops in cyanuric acid levels will affect the dosing of chlorine.
Why is this important:
Cyanuric Acid protects free chlorine from UV light. Without stabiliser, UV breaks down free chlorine, so that it only remains in the water for a matter of hours. Cyanuric acid protects free chlorine and allows it to remain in the water for much longer, 24 hours or more.
If stabiliser is too low, chlorine will not remain in the pool long enough to sanitise the water, chlorine requirements will be drastically increased, and chlorine levels will decrease rapidly.
If stabiliser is too high, the chlorine will be less effective and slower to inactivate algae, bacteria, viruses and other pathogens. This will result in poor sanitisation of the pool. As high stabiliser levels reduce the effectiveness of chlorine this will also reduce ORP readings.
How to increase Cyanuric Acid levels
Cyanuric acid is increased by adding to products containing it to the pool. Most commonly, this is done by adding Chlorine Stabiliser (cyanuric acid) via the skimmer box with the pump running.
How to add stabiliser
- Before adding remove any filter or skimmer socks and clean the filter.
- Turn on circulation pump.
- Add the required amount via the skimmer box. It is important to quickly mix it in as much as possible before it can form into rocks which take time to dissolve. The rocks will form more rapidly in cold water.
- Leave the equipment running until the stabiliser is fully dissolved.
How much should I add?
You will need to calculate how much to add with the following formula or talk to your local pool expert.
What you will need:
- Cyanuric Acid Test Result (PPM)
- Ideal Cyanuric Acid Level (PPM)
- Pool Volume (Litres)
- QTY Required to increase 10,000L by 1ppm (Grams) - see the product packaging for details
Formula:
(Ideal Cyanuric Acid Level - Cyanuric Acid Test Result) / Pool Volume / 10,000 x QTY Required to increase 10,000L by 1ppm
= grams to add
Example:
- Cyanuric Acid Test Result = 20
- Ideal Cyanuric Acid Level = 30
- Pool Volume = 20,000L
- QTY Required to increase 10,000L by 1ppm = 20g
= (30 - 20) x 20,000 / 10,000 x 20
= 10 x 2 x 20
= 20 x 20
= 400 grams cyanuric acid
How to decrease Cyanuric Acid levels
Decreasing cyanuric acid levels is a tricky and costly process and it is much easier to prevent the problem.
To decrease cyanuric acid levels you can use one of two methods:
1) Add a bioactive product which will consume the cyanuric acid in the water
- This option is the fastest but is not always effective. The product is also quite expensive.
- Consult with your local pool expert on whether this option would be suitable for you.
2) Dilute the water
- By removing water from the pool and adding freshwater you can dilute the cyanuric acid in the water. This will also dilute other chemicals in the pool.
- This can be done in one go or you can allow it to dilute through normal water loss over time, if the levels are still within safety limits.
- If diluting over time, avoid adding any products that contain cyanuric acid
Differentiation
Stabiliser is one of the most difficult and confusing products to differentiate as it comes under a lot of different names and may be combined with a lot of different products. In general, I look at the active ingredients to determine whether the product contains stabiliser. Any product containing stabiliser should mention cyanuric acid or isocyanurate.
Stabiliser, Chlorine Stabiliser, Isocyanurate and Cyanuric Acid
These are all different names for the same product. This product may also be packaged under other names such as UV block-out or Sunblock. To tell if this is the same product check that the Active Ingredient is Isocyanurate or Cyanuric Acid.
Dichlor Isocyanurate or Sodium Dichloroisocyanurate Dihydrate
This is a type of chlorine compound which contains stabiliser. Usually 56% Chlorine and up to 44% stabiliser.
Trichlor Isocyanurate
This is a type of chlorine compound which contains stabiliser. Usually 90% Chlorine and up to 10% stabiliser.
Stabilised Chlorine
This is another name for either Dichlor Isocyanurate or Trichlor Isocyanurate. It may be marketed as 2-in-1 chlorine, 3-in-1 chlorine or in a number of other names.
