Cold water changes everything. As temperatures slide, algae take a back seat, chlorine demand dips, and the Langelier Saturation Index tilts toward corrosive—quiet shifts that can quietly chew through plaster and equipment if you are not paying attention. We sit down with industry legend Bob Lowry to map a simple, reliable winter playbook that protects the vessel, extends gear life, and saves money when demand is low.

We start with the biology: algae reproduction slows around 55°F, which means you can safely run lower free chlorine. But that win comes with a catch—temperature drags LSI downward, so water gets hungrier for calcium. Bob explains how a small bump to pH and total alkalinity can stabilize balance without chasing numbers, and why calcium hardness targets still matter even in the off-season. We talk through the practical side, from long gauntlet gloves that make cold work bearable to smarter run-time choices. If you are tempted to run the pump two hours “just because,” hear why that middle ground is worse than a proper turnover.

Cyanuric acid gets special attention. After a summer of tabs, winter is the perfect time to lower CYA with a partial drain and refill. Bob also shares why CYA may drift down on its own—and in rare cases crash—due to specific bacteria when chlorine is low. The takeaway is simple: even in winter, test with intent, keep CYA in the 30–50 ppm sweet spot, and nudge LSI back to balanced as temperatures fall.

• Cold water reduces chlorine demand and slows algae growth
• LSI drops with temperature, raising corrosion risk
• Open vs closed pool choices by climate and power reliability
• Salt generators underperform below about 60°F
• Effective winter circulation strategies and freeze protect
• Partial drain to reduce high CYA from summer tabs
• Rare bacteria can consume cyanuric acid in low-chlorine pools
• Preventing stains, rings, and surface damage during dormancy
• Practical tweaks: raise alkalinity with bicarb, monitor pH and calcium
• Cost control in winter with lower chemical usage

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