You can swim in a pool with high CYA levels as stabilizer itself isn't harmful, but high CYA reduces chlorine effectiveness, making it harder to maintain proper sanitization. The real concern is whether you can maintain adequate free chlorine levels.
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Yes, you can swim in a pool with high CYA (cyanuric acid) levels from a toxicity standpoint - CYA itself is not harmful to swimmers. However, high CYA levels significantly reduce chlorine effectiveness, making it extremely difficult to maintain proper sanitization. The real question isn't whether CYA is safe, but whether you can maintain adequate free chlorine levels to keep the pool sanitized.
CYA, also known as pool stabilizer or conditioner, is designed to protect chlorine from UV degradation. While beneficial in proper amounts (30-50 ppm for regular pools, 70-80 ppm for salt water generators), levels above 100 ppm create significant challenges for pool maintenance.
The issue with high CYA isn't the stabilizer itself - it's what it does to your chlorine. As CYA levels increase, you need progressively higher free chlorine (FC) levels to achieve the same sanitizing effect. At 100 ppm CYA, you'd need to maintain at least 7.5 ppm FC for basic sanitation. At 150 ppm CYA, this jumps to over 11 ppm FC.
Swimming is generally safe when you can maintain the proper FC/CYA ratio, regardless of how high your CYA is. Use the FC/CYA chart to determine your minimum FC level:
Test your water with a quality test kit like the Taylor K-2006C to get accurate readings. Never rely on test strips for CYA measurements.
Do not swim if you notice any of these conditions, especially with high CYA:
High CYA makes it much harder to shock the pool and kill contaminants, so these warning signs are more serious than in a properly balanced pool.
While technically possible to swim safely with high CYA, the practical challenges are significant:
You'll use 2-3 times more liquid chlorine to maintain proper FC levels. This dramatically increases operating costs and makes routine maintenance more expensive.
When problems occur, SLAM (Shock Level And Maintain) treatment becomes extremely expensive and time-consuming. You might need to maintain 20+ ppm FC for days or weeks to clear issues.
You'll need to test FC levels daily, as the high chlorine demand makes levels drop quickly. Missing even a day of testing could allow problems to develop rapidly.
Rather than managing high CYA indefinitely, consider these solutions:
The most cost-effective long-term solution is partially draining and refilling your pool. Drain 1/3 to 1/2 of the water and refill with fresh water. This immediately reduces CYA levels proportionally.
For extremely high CYA (200+ ppm), complete water replacement may be most economical. Calculate the cost of water versus months of excessive chlorine usage.
Commercial CYA reducers exist but are expensive and work slowly. They're typically only cost-effective for smaller pools or when draining isn't possible.
To avoid high CYA in the future:
You can swim in a pool with high CYA if you can maintain proper FC levels according to the FC/CYA chart and the water remains clear and properly sanitized. However, the practical challenges and costs usually make it worth addressing the high CYA through partial water replacement rather than managing it long-term. Always prioritize water clarity and proper FC levels over convenience when making swimming decisions.
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