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Sources and formulas

Water targets

• CDC: home pool and hot tub water treatment and testing. Chlorine, pH, testing frequency, and hot tub advice.
• CDC Model Aquatic Health Code, 2023. Total alkalinity and calcium hardness limits. It is written for public pools, so treat it as outer limits.
• Hayward: how much salt does the system require? AquaRite salt range.

Ranges described as "common targets" are everyday pool-care practice and do not come from a health authority. The chlorine-to-stabilizer ratios (7.5% and 40% of CYA) are rules of thumb from the Trouble Free Pool community. Our sand, hot tub and Olympic depth figures come from maker and dealer listings, and those sometimes disagree: the pages say so where it matters.

Formulas

10,000 US gallons = 37,854 liters, and 1 ppm = 1 mg per liter.

• Salt, CYA: ppm × liters ÷ 1,000 = grams of the pure substance.
• Chlorine: the same, divided by the product's available chlorine. Liquid strength is treated as grams per 100 mL.
• Baking soda: 10 ppm alkalinity (as CaCO3) is 0.2 meq/L, at 84 mg per meq: 1.40 lb per 10,000 gallons.
• Muriatic acid: 31.45% is about 10 mol/L, so 10 ppm in 10,000 gallons takes about 26 fl oz.
• Calcium chloride: 77% flake, taken as the dihydrate: 10 ppm in 10,000 gallons takes about 1.2 lb.
• pH doses: the carbonate system at constant dissolved carbonate (pK1 6.2, pK2 10.1). These ignore stabilizer and borates, so they are estimates.
• Volume: 7.48 gallons per cubic foot.

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