Most pool pros have heard it for years: lower the pH to make chlorine stronger. That’s true in non-stabilized water, but once cyanuric acid enters the picture, the rules change. We sit down with Eric Knight to unpack why the FC-to-CYA ratio, not pH, governs chlorine’s effective strength in outdoor pools—and how that insight can save you time, money, and a lot of acid.

We break down the chemistry in plain language. You’ll hear how chlorine splits into hypochlorous acid and hypochlorite ion, why that balance matters indoors, and how CYA binds most chlorine outdoors to form isocyanurates. With typical CYA levels, the effective kill speed stays nearly the same between pH 7.0 and 8.0, which means chasing an ultra-low pH for “stronger chlorine” is a dead end. Instead, use pH to manage balance on the Langelier Saturation Index, contain its rise with smart alkalinity and calcium hardness, and aim for a CYA level that keeps your free chlorine target achievable.

We also talk real-world strategy: the pitfalls of overstabilization, how high CYA inflates contact times, and why partial drains are sometimes the only fix. To sharpen your program, support chlorine with enzymes to trim oxidant demand, control phosphates to lower growth pressure, and consider secondary oxidation where it fits. The goal is a stable chain: CYA in range, free chlorine matched to that CYA, pH contained for LSI, and demand reduced so sanitizer can do its job.

• FC-to-CYA ratio as the primary driver of chlorine effectiveness in outdoor pools
• Why pH control matters for LSI balance more than sanitization with CYA present
• The equilibrium of HOCl and OCl− in non-stabilized water contrasted with CYA-bound chlorine
• Practical CYA ranges and why levels above 50 ppm complicate free chlorine targets
• Overstabilization risks, longer contact times, and when to drain and dilute
• Using enzymes, phosphate control, and secondary oxidizers to reduce oxidant demand
• Containing pH with LSI strategy instead of forcing low numbers that rebound
• Clear differences between sa

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