Pool stabilizer (cyanuric acid/CYA) does not evaporate from your pool water. Unlike chlorine, stabilizer remains in the water indefinitely and can only be removed through dilution, backwashing, or complete water replacement.
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No, pool stabilizer (cyanuric acid or CYA) does not evaporate from your pool water. Unlike free chlorine which dissipates quickly from UV rays and evaporation, stabilizer remains dissolved in the water indefinitely. This is actually one of the most common misconceptions among pool owners and explains why many pools become over-stabilized over time.
First, let's diagnose what's happening with your pool stabilizer levels. Many pool owners assume their stabilizer disappears like chlorine does, but the reality is quite different. If you've been adding stabilizer regularly thinking it evaporates, you likely have dangerously high CYA levels that are making your chlorine ineffective.
Before making any adjustments, you need to know your exact cyanuric acid level. Use a reliable test method like the Taylor K-2006C test kit turbidity test or CYA test strips. The ideal range is 30-50 ppm for traditional chlorine pools and 70-80 ppm for salt water generator pools.
Understanding the chemistry helps explain why stabilizer behaves so differently from chlorine. Cyanuric acid forms a protective bond with free chlorine molecules, creating chloramines that resist UV degradation. This chemical bond is stable and doesn't break down under normal pool conditions.
Since stabilizer doesn't evaporate, it accumulates in your pool water over time. Every time you add stabilized chlorine products (dichlor, trichlor, or stabilizer directly), you're increasing your CYA level permanently. This is why many pools end up with CYA levels above 100 ppm, rendering chlorine nearly useless.
If your CYA is above 50 ppm (or 80 ppm for SWG), you'll need to dilute. The formula is: (Current CYA - Target CYA) ÷ Current CYA = Percentage of water to replace. For example, if your CYA is 100 ppm and you want 50 ppm: (100-50) ÷ 100 = 50% water replacement needed.
Most pools need stabilizer added only once per season, typically 1 pound of cyanuric acid per 3,000 gallons to achieve 30 ppm. Add it slowly through the skimmer with the pump running, or dissolve it in a bucket first. Retest after 24-48 hours of circulation.
To prevent over-stabilization, use liquid chlorine (sodium hypochlorite) for regular sanitizing and shock treatments. Save stabilized chlorine products for specific situations or use them sparingly. Cal-hypo shock is another good option that doesn't add CYA.
If you discover your CYA is too high, you'll notice these symptoms:
High stabilizer levels require proportionally higher chlorine levels. With CYA at 80 ppm, you need at least 6 ppm free chlorine for basic sanitation. This becomes expensive and impractical, which is why maintaining proper CYA levels is crucial.
The best approach is preventing over-stabilization from the start. Test CYA monthly during pool season and annually before opening. Keep detailed records of what products you add, as many contain hidden stabilizer.
Safety warning: Never add cyanuric acid directly to pool water in large quantities. It can create dangerous pH swings and doesn't dissolve quickly, potentially causing equipment damage.
If your CYA is extremely high (over 150 ppm) or you're struggling with persistent algae problems, consider professional water testing and treatment. Sometimes a complete drain and refill is the most cost-effective solution.
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