Bob Lowry Why High Cyanuric Acid Makes Chlorine Weak

Show Notes

Your pool can test “fine” on chlorine and still struggle to stay clear, safe, and algae-free. The missing piece is often cyanuric acid (CYA), the stabilizer that protects chlorine from UV sunlight but also controls how much chlorine is actually active at any moment. When CYA climbs too high, the kill speed drops, problems linger longer, and the fix is rarely just “add more chlorine.” 

We walk through what cyanuric acid is, why the pool industry embraced it, and the chemistry most people never hear: the majority of chlorine becomes bound to CYA, leaving only a small percentage immediately available. That equilibrium can be a benefit at normal levels, but it turns into a liability at 100, 150, or 200 ppm, where effectiveness falls off a cliff. We also dig into how CYA influences overall water balance, including pH buffering and why adjusted alkalinity matters when you’re thinking about LSI and avoiding scale or corrosion. 

Then we get practical. If CYA doesn’t evaporate, how does it ever go down, and why does it seem to rise every summer? We connect stabilized chlorine tablets, ongoing chemical additions, and the reality that only real water loss lowers CYA. We compare partial drain and refill with alternative methods like alum floc, including the labor, cleanup, and rebalancing that can follow. 

If you want better pool water chemistry, stronger chlorine effectiveness, and fewer recurring problems, listen through, then subscribe, share this with a pool owner or pool service pro, and leave a review with your biggest CYA question.

We break down why cyanuric acid (CYA) helps chlorine survive sunlight but can also make chlorine far less effective when the level gets too high. We explain the chemistry in plain terms, then walk through the most realistic ways to bring CYA back down and keep it from creeping up again.
• why the industry calls cyanuric acid a stabilizer and conditioner
• how sunlight destroys unstabilized chlorine and why CYA changed pool service
• what it means when chlorine bonds with CYA and stays in equilibrium
• how high CYA slows kill speed even with “good” chlorine readings
• why CYA affects pH buffering and adjusted alkalinity calculations
• why drain and refill is the simplest reliable CYA reduction method
• how alum floc works, the cleanup hassle, and concerns about leftover aluminum
• why CYA does not evaporate and keeps building without real water loss
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