Many pool owners don’t fully understand what cyanuric acid does to pool water. When they test the pool water to find it’s indicating a high or low level of cyanuric acid they usually ignore the test. After all, the pool water looks clear and clean so they assume everything is good.
When the pool water has a higher than normal level of cyanuric acid, or pool stabilizer chemical, it will reduce the chemical effectiveness of chlorine leaving your pool unsanitized and exposed to bacteria, viruses and other contaminants.
Adding more chlorine will have little effect because it will be neutralized by the excessive level of cyanuric acid.
The best way to reduce the concentration of stabilizer is to drain some water from the pool and refill with fresh water.
Table of Contents
What is Cyanuric Acid?
Cyanuric Acid (CNOH) is commonly marketed as “pool stabilizer”, “pool conditioner” or “pool sunscreen”. It’s produced as a white, odorless, solid, and granular or powder compound that is fairly safe to handle, however, we always recommend wearing gloves with pool chemicals and washing your hands afterwards.
Chlorine is a highly reactive element and dissipates rapidly in water. Pool stabilizer works by binding to the free chlorine in water and slowing down the reaction of chlorine to extend its chemical lifespan.
In the summer the sun is hot and ultra-violet radiation peaks. Free chlorine can be rapidly burned away, in a matter of hours, leaving the water unsanitized. Unstabilized chlorine can evaporate away in a morning leaving the pool unsafe for swimming in the afternoon.
It is essential to add cyanuric acid to the water to stabilize and extend the chlorine’s useful life in the pool. Stabilized chlorine will last 3 to 4 times longer than unstabilized chlorine.
Note: Do not add cyanuric acid (stabilizer) to hot tubs or spa pools that are sanitized with bromine. Bromine is not able to be stabilized. Bromine is only recommended for spas and hot tubs because it works well at higher temperatures. Adding Bromine to a pool doesn’t work well as it would quickly burn off in the sun.
How to Test for Cyanuric Acid in Pools
Most quality swimming pool test kits and strips have a test indicator for cyanuric acid. Make sure you have a test kit or strips designed for a chlorinated pool and not for bromine, ozone or ionized sanitized pool.
I recommend taking two samples of water from the pool when testing. One from the deep end and one from the shallow making sure you collect the sample from at least elbow depth of water. Use an up turned clear plastic cup to gather your sample. You can see it’s full of air when you place it in the water and turn it over at elbow depth to collect the water sample.
Some pool owners like to test with both a chemical kit and strips to compare the result. These days the test strips are very accurate and reliable. I would recommend using the strips as they are cheaper, simpler to use and easier to match test result color against the color chart to make the reading.
What Causes Cyanuric Acid to be High in a Pool?
What causes cyanuric acid to be high in a pool is adding to much stabilizer.
A pool owner could make a mistake, not read the instructions correctly, and add too much stabilizer to the pool. But more commonly cyanuric acid becomes high when the wrong type of chlorine is added to the pool.
This happens when stabilized chlorine is added to the pool. Stabilized chlorine products are manufactured with cyanuric acid mixed into the product.
If your cyanuric acid level is already within the normal range, 30 – 80 ppm, and you add stabilized chlorine you will overdose the pool with stabilizer.
Do I Need to Add Stabilizer to my Pool?
If you have an indoor pool that is fully shaded from the sun you do not need to add cyanuric acid (pool stabilizer) to your pool. The free chlorine in the water will stay active longer than an outdoor pool because there is no UV light to dissipate the chlorine.
If you have a salt water outdoor pool you will need to manually add stabilizer to the pool. The salt chlorinator will produce chlorine when the pump is running. But without stabilizer the chlorine will evaporate and dissipate quickly.
If you have a fresh water pool you will need to add chlorine and stabilizer. You can add them separately or use a stabilized chlorine product that contains cyanuric acid.
Note: The danger with stabilized chlorine products is that you can overdose the pool with too much stabilizer. This will reduce the effectiveness of chlorine. Always test your water to ensure you have the correct chemical levels.
Is it safe to swim in a pool with high cyanuric acid?
The cyanuric acid isn’t the issue here. The problem is the high level of stabilizer will inactivate your free chlorine and leave your pool unsanitized. Never swim in a pool that is unsanitized as you will be exposed to bacteria, viruses and other contaminates.
Does Stabilizer Lower pH?
No. Cyanuric acid will have little effect on a swimming pools pH. It’s a fairly safe chemical at low concentrations.
If you want to lower pH you need to add muriatic acid (or hydrochloric acid) to the pool water, recirculate with the pump and retest.
Does Stabilizer Raise pH?
No. Cyanuric acid has little effect on raising the pH of pool water and is a fairly safe chemical at low concentrations.
If you want to raise pH you need to add a product containing sodium carbonate or sodium bicarbonate to the pool water. Always let the water recirculate with the pump and retest.
How to Lower Cyanuric Acid in a Pool
When you test your pool water and find the cyanuric acid (stabilizer) level is too high you need to dilute the level. You have three options:
- Buy a Stabilizer reducer product.
- Drain some water from your pool and refill with fresh water to dilute the water.
- Wait for rain to dilute the pool water.
When draining pool water you should only need to drain off the level down to the bottom of the skimmer box and refill. This should reduce the cyanuric acid level by 5 to 10%.
If your cyanuric acid level is very high you will need to drain much more water out of your pool. Try draining one quarter or one third of the water from the pool and refill.
Note: When you refill a pool with tap water or water from another source it may unbalance the other chemical components of your pool water. You need to retest everything and adjust the levels as required.
Note: If you are finding your cyanuric acid level is high I recommend you don’t use stabilized chlorine products so that you are in full control of your cyanuric acid level.
How to Raise Cyanuric Acid in a Pool
Simply add more pool stabilizer to the pool water. Increase the level of cyanuric acid to the recommended level of 30 – 80 ppm. Please follow the instructions on the product label.
If it’s the off season and you don’t swim in the pool because it’s too cold then you are safe with a low level of stabilizer at 30 or 40ppm. If you have a pool cover then your chlorine will be protected from the sun. So you will only need a lower level of stabilizer in the water.
During the hot summer season increase the level to 70 or 80ppm. This protects the chlorine against the sun. The best time of day to add any chemical to pool water is in the early evening just as the sun is going down. This will ensure the chemical is not affected by UV light and heat giving the chemical time to work overnight. Also you need to ensure that the pump is going to run for at least three or four hours to thoroughly circulate the water and mix in the chemicals.
The most important thing to remember is to slowly increase the level of cyanuric acid. Then retest the water after it has dissolved and circulated around the pool. I always add half the recommended dosage of stabilizer, retest and later add some more. It’s better to be safe than sorry because if you add too much it is difficult to reduce the level. You normally have to drain some water from the pool, refill and rebalance all the other chemicals.
Final Thoughts
Cyanuric acid is a very simple chemical to understand in regard to swimming pools sanitized with chlorine products. It simply makes the chlorine last longer by preventing chlorine from evaporating in the hot sun. This is most important in the hot summer season when chlorine can burn off in a few hours. The longer the chlorine stays in the pool the better the sanitation of the pool.
To prevent overdosing of cyanuric acid add it separately from chlorine and do not use stabilized chlorine products. If you add to much chlorine it’s not usually a problem. The sanitation process will consume the excess chlorine. Too much stabilizer is a problem as it won’t go away by itself.
