If your pool chlorine keeps disappearing even though you’re dosing it regularly, low cyanuric acid is almost certainly the culprit. Cyanuric acid (CYA) \u2014 also called pool stabilizer or conditioner \u2014 is what shields chlorine from UV rays. Without enough of it, sunlight destroys free chlorine within a few hours. You end up dumping chemical after chemical into your pool with nothing to show for it.<\/p>\n
<\/p>\n Pool Cyanuric Acid Too Low: How to Fix It and Protect Your Chlorine: If your pool chlorine keeps disappearing even though you\u2019re dosing it regularly, low cyanuric acid is almost certainly the culprit. Cyanuric acid (CYA) \u2014 also called pool stabilizer or conditioner \u2014 is what shields.<\/p>\n<\/section>\n <\/p>\n The good news: fixing low CYA is straightforward once you know your current level and your pool’s volume. This guide walks you through everything \u2014 why CYA drops, how to test it, exactly how much stabilizer to add, and how to avoid overdoing it.<\/p>\n Chlorine breaks down fast under UV light \u2014 we’re talking 50\u201390% loss in a matter of hours on a sunny day if there’s no CYA in the water. Cyanuric acid forms a protective bond with chlorine molecules that dramatically slows that degradation without affecting chlorine’s ability to sanitize.<\/p>\n Think of CYA as sunscreen for your chlorine. You wouldn’t send people out in direct summer sun without sunscreen; don’t send chlorine into your pool without stabilizer.<\/p>\n The ideal CYA range for most outdoor pools is 30\u201350 ppm<\/strong> (parts per million). For saltwater pools, many pool pros recommend a slightly higher target of 60\u201380 ppm<\/strong> since salt cells produce chlorine continuously and need more protection.<\/p>\n CYA doesn’t evaporate, but several things reduce it:<\/p>\n If your CYA reads below 30 ppm, you’re running unstabilized chlorine. Your sanitizer is getting eaten alive by the sun.<\/p>\n CYA doesn’t show up on basic test strips \u2014 you need either:<\/p>\n Turbidity test (pool store strips or kit):<\/strong> Add a reagent to a water sample. The solution clouds up and you match the turbidity to a scale. These give you a rough reading in the 0\u2013100 ppm range.<\/p>\n Liquid reagent test kit:<\/strong> More accurate. Taylor K-2006<\/a> is the gold standard that pool techs use. It includes a CYA turbidity test and reads more precisely than strips.<\/p>\n Pool store water test:<\/strong> Free or cheap at most pool stores. They run a full panel including CYA. Reliable, though you’re trusting their equipment calibration.<\/p>\n Test CYA every 2\u20134 weeks during swim season, and always after a significant water change.<\/p>\n The calculation depends on your pool’s volume in gallons and how much you need to raise CYA.<\/p>\n General rule:<\/strong> 13 oz of cyanuric acid raises CYA by approximately 10 ppm in a 10,000-gallon pool.<\/p>\n Here’s a quick reference table:<\/p>\n | Pool Size | Raise CYA by 10 ppm | Raise CYA by 20 ppm | Raise CYA by 30 ppm |<\/p>\n |———–|———————|———————|———————|<\/p>\n | 10,000 gal | ~13 oz | ~26 oz | ~39 oz |<\/p>\n | 15,000 gal | ~20 oz | ~40 oz | ~60 oz |<\/p>\n | 20,000 gal | ~26 oz | ~52 oz | ~78 oz |<\/p>\n | 25,000 gal | ~32 oz | ~65 oz | ~97 oz |<\/p>\n Don’t eyeball this. Adding too much CYA creates its own problem \u2014 high CYA locks up chlorine and makes it ineffective (a condition called “chlorine lock”). It’s much easier to raise CYA than to lower it, so add slightly less than you think you need, wait a few days, then retest.<\/p>\n > Dealing with low CYA and other chemistry imbalances at the same time?<\/strong> The Pool Chemical Calculator app<\/a> gives you exact dosing for your pool size and current readings \u2014 including cyanuric acid, chlorine, pH, alkalinity, and calcium. Enter your numbers and get a specific treatment plan in seconds. Free on iOS and Android.<\/p>\n What you’ll need:<\/strong><\/p>\n Steps:<\/strong><\/p>\n 1. Test your current CYA<\/strong> \u2014 You need a baseline. If you don’t have a number, take a sample to the pool store before adding anything.<\/p>\n 2. Calculate the dose<\/strong> \u2014 Use the table above or the Pool Chemical Calculator app. Subtract your current CYA from your target (aim for 40 ppm as a middle ground) to find how many ppm you need to add.<\/p>\n 3. Pre-dissolve the stabilizer<\/strong> \u2014 CYA granules dissolve slowly. Add them to a bucket of warm pool water and stir until dissolved. Never add dry granules directly to the skimmer \u2014 they can clog the basket and damage the pump if they clump.<\/p>\n 4. Add to the pool<\/strong> \u2014 Pour the dissolved solution slowly around the perimeter of the pool, near the return jets if possible to help it circulate.<\/p>\n 5. Run the filter<\/strong> \u2014 Keep it running for at least 24 hours to distribute the CYA evenly throughout the water.<\/p>\n 6. Wait before retesting<\/strong> \u2014 CYA takes 24\u201348 hours to fully dissolve and register accurately on a test. Retest before adding more.<\/p>\n 7. Don’t shock immediately after adding CYA<\/strong> \u2014 Give it a day. High chlorine can interfere with CYA’s ability to stabilize properly when both are being introduced at the same time.<\/p>\n If you’re experiencing any of these, low CYA is worth testing:<\/p>\n When CYA is low, you’re fighting the sun every single day. Fix the CYA first \u2014 everything else gets easier after that.<\/p>\n High CYA (above 100 ppm) is a real problem. It binds too tightly to chlorine and prevents it from sanitizing effectively \u2014 even if your free chlorine tests at 3\u20134 ppm, you can get algae because the active fraction of chlorine is suppressed.<\/p>\n There’s no chemical fix for high CYA. The only solutions are:<\/p>\n This is why precision matters when adding stabilizer. Get close to your target, not past it.<\/p>\n Once you have CYA dialed in, your chlorine target changes. Higher CYA means you need proportionally more free chlorine to maintain the same sanitizing power. This is the relationship pool techs call the “FC:CYA ratio.”<\/p>\n | CYA Level | Minimum Free Chlorine |<\/p>\n |———–|———————-|<\/p>\n | 20 ppm | 1 ppm |<\/p>\n | 30 ppm | 1.5 ppm |<\/p>\n | 40 ppm | 2 ppm |<\/p>\n | 50 ppm | 2.5 ppm |<\/p>\n | 70 ppm | 3.5 ppm |<\/p>\n | 80 ppm | 4 ppm |<\/p>\n Keep your free chlorine at or above these minimums to maintain proper sanitation. A Taylor test kit like the K-2006<\/a> measures both \u2014 making it easy to confirm the ratio is in good shape.<\/p>\n <\/p>\nQuick answer<\/h2>\n
\nWhat Cyanuric Acid Actually Does<\/h2>\n
\nWhy Your CYA Gets Too Low<\/h2>\n
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\nHow to Test Cyanuric Acid Levels<\/h2>\n
\nHow Much Cyanuric Acid to Add<\/h2>\n
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\nStep-by-Step: How to Raise CYA in Your Pool<\/h2>\n
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\nSigns Your CYA Is Too Low<\/h2>\n
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\nWhat Happens If You Overshoot CYA?<\/h2>\n
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\nCYA and Chlorine Interaction: The Minimum FC Table<\/h2>\n
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