Cyanuric Acid: The Sunscreen for Your Pool
Balancing Stabilizer levels for effective chlorine performance.
If you have an outdoor pool, the sun is your chlorine's greatest enemy. Without protection, UV rays can destroy 90% of your free chlorine in just a few hours. Cyanuric Acid (CYA), often called 'Stabilizer' or 'Conditioner,' acts as a sunscreen for your chlorine, holding it in the water until it's needed to kill bacteria. But like anything in pool chemistry, too much of a good thing can be a disaster.
The Chlorine-CYA Relationship
CYA works by forming a weak chemical bond with the chlorine, shielding it from UV light. The ideal level for a non-saltwater pool is 30-50 ppm. At this level, you get the best protection without hindering the chlorine's ability to sanitize. However, as CYA increases, you must also increase your target chlorine level to maintain the same killing power.
The Danger of 'Over-Stabilization'
When CYA levels exceed 80-100 ppm, 'Chlorine Lock' occurs. The CYA holds onto the chlorine so tightly that it can't kill algae or bacteria effectively. You might have 10 ppm of chlorine in the water, but the pool still turns green. The only practical way to lower CYA is to drain a portion of the pool and refill it with fresh water.
How CYA Enters Your Pool
CYA doesn't evaporate. Once it's in the pool, it stays there. The most common source of high CYA is the use of 'stabilized' chlorine pucks (Trichlor) or shock bags (Dichlor). Each pound of these chemicals adds significant amounts of CYA. Over a single summer, a pool owner using only pucks can easily drive their CYA from 30 to over 150 ppm without realizing it.
The 7.5% Rule for Maintenance
To keep your pool safe and algae-free, your Free Chlorine (FC) should be at least 7.5% of your CYA level. If your CYA is 40, your minimum FC is 3 ppm. If your CYA is 100, your minimum FC jumps to a staggering 7.5 ppm! This is why keeping CYA in the 'Goldilocks' range (30-50 ppm) is so important for manageable maintenance and cost-effective chemical use.
FAQ
How do I add Cyanuric Acid?
CYA dissolves very slowly. The best way is to put the granules in a clean sock and hang it in front of a return jet, squeezing it occasionally. Avoid throwing it directly into the skimmer as it can take days to dissolve and may clog your filter.
Does indoor pool water need Stabilizer?
No. Indoor pools are protected from UV light. Adding CYA to an indoor pool only reduces the effectiveness of the chlorine without providing any benefit.
Can I use a chemical to lower CYA?
There are 'CYA reducers' (biological enzymes) on the market, but they are expensive and often unreliable. Draining and refilling is still the fastest and most dependable method.