Chlorine Stabilization

What is Cyanuric Acid?

Cyanuric acid is used in outdoor pools to protect chlorine from destruction by the sun’s UV rays. Sold commercially as “Pool Conditioner” or “Pool Stabilizer”, cyanuric acid sales amount to millions of metric tons per year for swimming pools and water treatment facilities.

Cyanuric Acid, or CYA as it is sometimes called, also saves millions of dollars in chlorine cost for pool operators and pool owners, who add it directly to the pool water, in a granular, flake or liquid form. Once added to the pool water, it seeks out and bonds to Free Chlorine molecules, reducing their activity, and thereby reducing the ability of UV rays to destroy the molecule.

Cyanuric acid is also used by pool chlorine manufacturers to create chlorinated cyanurates. Sodium Dichlor pool shock is a stabilized form of granular chlorine, a compound formed of sodium salts. Trichlor tablets are produced by further chlorinating the Dichlor into Trichlor compounds, and pressing them into a tablet. These pre-stabilized chlorinated cyanurate products contain a small amount of cyanuric acid, which is added to the pool as the chlorine is released.

What is the Best Level for pool stabilizer?

Swimming pool operators should maintain a level of 10-20 ppm on a shady pool and 20-40 ppm on a sunny pool. The pool should be diluted with fresh water if the cyanuric acid level exceeds 50 ppm. Too much pool stabilizer will reduce the power of your chlorine, and require more free chlorine levels to ensure full sanitation.

How much is too much pool stabilizer?

As mentioned above, when cyanuric acid tests show 50 ppm or higher, it is advised to lower the level of cyanuric acid in the pool. Some of our earlier writings on the subject may suggest that 100 ppm is the top limit, and beyond that could result in “chlorine lock”. Newer thinking on the suppressive effect of cyanuric acid on chlorine’s killing power has us revising our top limit for CYA to 50 ppm, with a preferred range of 20-40 ppm.

How to lower pool stabilizer level?

Using a submersible pump, or your pool filter pump, drain a portion of the pool water, and add fresh (unstabilized) water to refill the pool. At 40 ppm, draining and refilling 25% of the water would lower the cyanuric acid level to 30 ppm. There is no chemical available that will remove or reduce cyanuric acid in pools.

If I use stabilized chlorine, do I need to add additional cyanuric acid?

Probably not, although many pool owners with sunny pools will see a strong benefit of having at least 10 ppm of base residual to start with. Over time, for pools that are not diluted by winterization or frequent rains, cyanuric acid may begin to build-up from the use of stabilized chlorine (Dichlor shock and Trichlor tablets). When draining and refilling a pool for repairs, add 1-2 lbs per 10000 gallons to start.

Does pool stabilizer make my chlorine less potent?

Yes, it does by making the molecule much less active and mobile, kind of sluggish. High pH levels in the pool can exacerbate the problem. Pools that use chlorine stabilizer should maintain a chlorine residual of 2 ppm, and when shocking the pool, add a double dose of shock.

Doesn’t that remove the benefit of using pool stabilizer?

If you have to keep your chlorine level twice normal level, and shock the pool twice as hard, it does remove much of the benefit of using pool stabilizer. However, in sunny pools without at least 10 ppm of cyanuric acid, the pool operator may have trouble even reaching 1.0 ppm of free chlorine.

Does pool stabilizer reduce the total alkalinity in my pool?

It doesn’t reduce it, but cyanuric acid in the pool contributes to a part of your total alkalinity reading and can cause you to believe that your alkalinity levels are higher than they really are. The formulas are complicated, but to compensate for cyanuric acid’s contribution to total alkalinity, subtract 1/3 of your cya level from your alkalinity level. For example, if your cya level is 30 ppm, subtract 1/3 or 10 ppm, from your alkalinity reading, to know your true TA level.

How is pool stabilizer tested for in pools?

A turbidity test is used as a cyanuric acid test for pool water. Taylor uses a vial with a black dot on the bottom. A water sample bottle is filled to the 25 ml line and an equal amount of cyanuric acid reagent is added which clouds the test sample in the presence of cyanuric acid. The mixed sample is added to the vial with the black dot, just until the black dot disappears in turbid, cloudy water. Then a cya reading can be taken on the side of the vial, at the water level. You can also use test strips to check cyanuric acid in pools or drinking water.

Related Product Pages:

Cyanuric Acid
Stabilized Chlorine Tablets
Stabilized Chlorine Shock

Related Blog Posts:

Cyanuric Acid: aka Conditioner or Stabilizer
Fresh Thoughts on Cyanuric Acid
Pool Stabilizer and Chlorine Kill Rates