Ever wonder why a pool can look fine one week and show stains, rough plaster, or a failing heater the next? The culprit is often low pH—water that turns aggressive, dissolves metals, and etches surfaces long before the damage is obvious. We walk through how acidic water behaves, where metals come from, and why stains show up only after the water hits its saturation point.

We dig into real-world service scenarios: vinyl and fiberglass pools that trend acidic because they lack buffering minerals, spa tubs that swing wildly depending on chlorine type and use, and the risky combo of low pH with cheap test kits that feed bad decisions. You’ll hear why investing in a reliable photometer that reads copper and iron saves you from surprise stains and equipment corrosion, plus a clear plan for when to use soda ash, borax, or baking soda. We also share a fast spa recovery routine: raise alkalinity first, then aerate to lift pH without overshooting.

Along the way, we challenge old chlorine wisdom. With cyanuric acid in play, the classic HOCl charts don’t tell the whole story. The smarter approach is keeping free chlorine appropriate to CYA while holding pH near 7.5 for swimmer comfort and stable balance. We cover borates as a pH buffer, how they affect alkalinity readings and the saturation index, and why soda ash lifts pH and alkalinity more strongly than bicarb when both are low.

• why low pH makes water aggressive
• etched plaster, corroded components, invisible metals
• saturation points leading to staining
• value of accurate copper and iron testing
• vinyl and fiberglass pH drift and tablet use
• spa chemistry, aeration, and quick rebalancing
• comfort thresholds for bathers around pH 7.5
• choosing borax, soda ash, or bicarb by goal
• borates’ impact on readings and stability
• chlorine effectiveness with cyanuric acid
• practical dosing plans and test habits

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