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How We Calculate

Every answer comes from these sums, the product strengths and the targets we use.

Volume

Multiply surface area by average depth, then by 7.48 gallons per cubic foot. A gallon equals 3.785 liters.

Chlorine

You need 1 gram of chlorine per 1,000 liters to raise free chlorine 1 ppm. The product strength is what we divide by: 12.5 or 10% for liquid chlorine, 8.25% for bleach, 65 or 73% for cal-hypo, and 56% for dichlor.

pH and alkalinity

The water's carbonate balance, at average alkalinity and stabilizer, sets the pH doses, using dry acid at 93.2% or muriatic acid at 31.45%. Alkalinity rises by the weight of the baking soda you add, per equivalent.

Equipment

To get pump flow, divide gallons by the turnover time. The filter math uses 20 GPM per square foot with sand, 2 with diatomaceous earth, and 0.375 with cartridge. For heater output, multiply gallons by 8.34 and by the rise, then divide by the hours.