CYAN URIC ACID
Common names:
"Conditioner"
"Stabilizer"

WHAT IS CYANURIC ACID ?

Chlorine in outdoor pools must be shielded from the degrading effects of the sun's ultraviolet (UV) rays. Cyanuric acid is used in outdoor pools with the inorganic chlorines such as calcium hypochlorite, sodium hypochlorite, lithium hypochlorite and chlorine gas.

It is recommended that the cyanuric-acid level be 30-50 ppm with a maximum of 100 ppm and a lower limit of 10 ppm. The level of cyanuric acid is reduced by dilution due to filter backwashing, bather dragout or dumping. To meet health codes, pools above 100 ppm need to be drained of about 20% of volume, and fresh water added. Four pounds of cyanuric acid will offer a reading of 50 ppm in 10,000 gallons of water. Cyanuric acid has a pH of 4.0, and if added to a gas-chlorinated pool, the addition of one-third of a pound of soda ash per pound of cyanuric acid is recommended.

'Chlorine Lock,' a term given to a condition once thought to be produced from high cyanuric-acid levels tying up free available chlorine, has been proven false by the industry. Generally, high cyanuric-acid levels of 400 ppm or higher are associated with excessive Total Dissolve Solids (TDS) or combined chlorine or chloramines and not "Chlorine Lock.'
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Beware of using 3" chlorine tablets excessively...

or any sanitizing product used in swimming pools that contain cyanuric acid. Cyanuric Acid, or what is commonly known as "conditioner" or "stabilizer." It is necessary to prevent chlorine from dissipating from the pool in matter of minutes due to the effects of sunlight. Conditioner in the water beyond the amounts of 30 ppm (parts per million) begin to "protect" the chlorine present in pool water. Too much which lessens chlorine's effectiveness and requires more chlorine to be added to do the same job as chlorine in water with less ppm of conditioner.

The popular three inch tablets my be very convenient to use but can create more problems than they solve. After awhile the tablets can contribute too much to the build up of Cyanuric Acid which can actually prevent chlorine's capacity for effective sanitization. These tablets work well until there is too much Cyanuric Acid build up in the water.

Beyond 30 ppm (parts per million) cyanuric acid becomes a deterrent rather than a help for allowing chlorine to do  it's job. Even though it keeps chlorine from dissipating from the water at an increased level, it does this so well that it even prevents the chlorine present in the water from effectively doing  it's job of killing bacteria and algae. A lot of pool men compensate  for this by continuing to add Cyanuric Acid inducing tablets and using algaecides on a constant basis. I have found that keeping the ppm for stabilizer down prevents me from having to add algaecides, ever. I use only inexpensive chlorine in small amounts as needed. Without all that conditioner in the way chlorine is able to quickly and effectively prevent and stop an algae bloom in it's tracks.

Also this is a very common problem which occurs when Stabilized Chlorine Granules are used. These contain a stabilizer, - Cyanuric Acid, - which reduces the destruction of chlorine by Ultra Violet light from the sun.

Although the Chlorine will be consumed, the Cyanuric acid will remain in the water, and every time that the pool is dosed with stabilized chlorine granules, the Cyanuric Acid level will increase.

The optimum level for Cyanuric Acid in swimming pool water is about 25 - 30 ppm. If the level is below that figure, more chlorine will be destroyed by sunlight than is necessary. BUT, - if the Cyanuric acid level increases above about 30 ppm, the chlorine becomes progressively OVER-stabilized, and its power of oxidation and disinfection is steadily reduced. Once the level exceeds 50 ppm the disinfection rate usually begins to noticeably fall.

This leads to a situation known as "Chlorine Lock". - Substantial levels of chlorine are present in the water, and are indicated on a test kit. But this Chlorine is "Locked up" by the high levels of Cyanuric Acid, and is unable to work normally.

Cyanuric Acid levels in pool water can only be controlled by dilution - ie, draining of some water and refilling with fresh. The best way to achieve this is during the weekly backwash cycle, by simply extending the backwash time, and then topping up with fresh water.

If a pool is in regular use, it is probable that about 5%, - or even more, of the pool volume has to be replaced each week in order to maintain the Cyanuric Acid content at an acceptable level.

It is a very good idea for pool owners to get a Cyanuric Acid test kit, - they are not expensive, - and monitor the levels each week. If the levels continue to rise, the backwash times can be extended until a stable level is maintained.

If the Cyanuric Acid level is above 50 ppm, and below 100 ppm - it is usually sufficient, to drain off about half the pool volume, and refill with fresh water. If the level is over 100 ppm it is a good idea to completely drain and refill the pool. Check with you pool Builder first, that emptying the pool will not cause any complications.

Trichlor chlorine tablets (3" Tablet) also contain Cyanuric Acid, though nowhere near as much as in the Stabilized Chlorine granules. Even so, it is still a good idea to monitor the levels of Cyanuric Acid in the pool water.
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TESTING FOR CYANURIC ACID (STABILIZER)

Cyanuric acid (CYA) is a common additive that stabilizes chlorine in outdoor swimming pools. If not carefully monitored, however, the concentration can build to a point that exceeds health codes. Dilution is the only way to reduce CYA levels. Draining a portion of the pool water and refilling with fresh source water will reduce concentrations.

The acceptable range of cyanuric acid is generally between 30 ppm and 100 ppm, 30 ppm to 50 ppm is best. CYA levels below 30 ppm substantially reduce the desired stabilizing property; levels above 100 ppm are prohibited by some health departments.

Testing for cyanuric acid is most commonly done with a turbidometric test, which uses a test reagent to precipitate the cyanuric acid and then uses the relative cloudiness (turbidity) of the reacted sample to gauge the CYA concentration.

A reagent called melamine is used. The melamine combines with the cyanuric acid in the water to form a fine, insoluble, white precipitate that causes the water to cloud in proportion to the amount of cyanuric acid in it. When the water clouds, it becomes more difficult to see an object in it.

Some CYA test kits contain a specially designed vial, which has a black dot painted in the bottom of it that is clearly visible when it is filled with water but becomes more difficult to see when the CYA has been precipitated. How much of the dot you can see is compared to a chart included in the CYA test kit to indicate the concentration in ppm.

 Other kits use a plastic rod with an angled piece that lies on the bottom of the vial and has a black dot painted on it. After the cyanuric acid has been precipitated, you raise the rod until the dot becomes visible, then read the CYA concentration from a set of numbers scribed on the side of the rod. The number closest to the level of the water in the test vial indicates the concentration in ppm.

There also is an electronic test instrument (spectropbotometer) used to read the relative turbidity of the sample. The newest method of CYA testing employs a dip-and-read test strip that is simply dipped into the pool water and changes color in about 30 seconds to indicate the level in ppm.

High levels of cyanuric acid will cause a reduced ORP reading. Manufacturers of ORP equipment recommend that a higher FAC be maintained to reach the desired 650 mV minimum.
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