Bob Lowry Explains Trichlor Tablets and Pool Acid Cautions

Think evaporation lowers cyanuric acid? Think again. We open the cover on persistent pool myths with help from the late Bob Lowry’s clear, data-driven explanations, and show how small assumptions can create big chemistry problems over a season.

First, we break down why CYA never leaves with evaporation—only pure water does. That means every trichlor tablet quietly stacks CYA week after week, often hitting 100 to 150 ppm in a single swimming season. We compare sanitizer byproducts in plain terms: trichlor and dichlor raise CYA, liquid chlorine nudges TDS via salt, and cal hypo increases calcium. You’ll hear practical numbers you can use on route, like how a gallon of liquid chlorine typically adds around 20 to 30 ppm salt depending on pool size, and how 65 percent cal hypo can add about 7 ppm calcium for every 10 ppm of free chlorine delivered.

Then we shift to acids. Muriatic acid remains the straightforward choice for lowering pH and alkalinity without adding sulfate. Dry acid, while convenient, introduces sulfate that can accumulate and lead to calcium sulfate scale—harder to remove than calcium carbonate and invisible to the LSI you rely on. We also cover why dry acid needs airtight storage due to deliquescence, how to approach dosing when total alkalinity runs high, and why older warnings about dry acid and salt systems don’t reflect current understanding, even if they persist in some manuals.

By the end, you’ll know how to choose the chlorine and acid strategy that fits your climate, hardness, and maintenance plan. 

• evaporation removes only pure water, not CYA
• trichlor adds 6 ppm CYA per 10 ppm chlorine
• CYA rises 25 ppm per month at common usage
• water loss from draining or splash removes CYA
• liquid chlorine adds modest salt and TDS
• all chlorine types end as part of TDS
• cal hypo adds about 7 ppm calcium per 10 ppm FC
• dry acid introduces sulfate and hidden scale risk
• calcium sulfate scale does not show on LSI
• dry acid is deliquescent and needs tight storage
• high alkalinity often needs muriatic for

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