How the Pool Calculations Work

Start with your pool gallons and a fresh water test. The gap to your chosen target sets the dose; pH estimates also use measured alkalinity and CYA to account for buffering. Match the formulation to your product label and retest before another addition, so the next estimate reflects your water’s response.

Salt

lb = Δppm × gallons × 8.34 lb/gal ÷ 1,000,000

This gives you the weight of sodium chloride needed to close the gap between your salt reading and target. Take the target and operating limits from your exact generator manual.

Example: 10,000 gal, salt from 2,800 ppm to 3,200 ppm; full estimated correction: 33.36 lb.

Dry chlorine / shock

oz by weight = ΔFC ppm × gallons × 8.34 × 16 ÷ (1,000,000 × available-chlorine fraction)

Use the label’s available-chlorine percentage for dosing. For example, 65% is 0.65 in the formula. Keep ingredient purity separate from available chlorine, and divide the result in ounces by weight by 16 to get pounds.

Example: 10,000 gal, a 1 ppm free chlorine increase, dry chlorine with 65% available chlorine: 2.053 oz by weight.

Liquid chlorine

fl oz = ΔFC ppm × gallons × 8.34 × 128 ÷ (1,000,000 × trade percent × 0.08345)

For liquid pool chlorine, enter the trade percent: 10 for 10%. That means grams of available chlorine per 100 mL of solution. Household bleach labels give sodium hypochlorite as a weight percent instead. The bleach calculation converts it using approximate solution density and the chlorine-to-hypochlorite molar-mass ratio.

Example: 10,000 gal, a 1 ppm free chlorine increase, liquid chlorine with 10% trade available chlorine: 12.79 fl oz.

pH down

acid equivalents = modeled alkalinity decrease in equivalents per litre × pool volume in litres

Your TA and CYA readings set the starting carbonate buffer in a closed-system model at 25°C. For liquid acid, the estimate uses HCl weight percent and density. Dry acid uses sodium bisulfate purity and molar mass. Each dose models a change of no more than 0.2 pH units. Your pool can respond differently because of aeration, temperature or buffers outside the model.

Example: 10,000 gal, pH from 8.0 to 7.8 in the first step, total alkalinity 100 ppm as CaCO₃, CYA 0 ppm, HCl 31.45% by weight: 3.709 fl oz.

pH up

Solve the carbonate/cyanurate equilibrium: each mole of Na₂CO₃ adds 1 mole of dissolved carbon and 2 equivalents of alkalinity.

Enter measured TA and CYA to estimate a dose of pure sodium carbonate (soda ash). Each step models a rise of no more than 0.2 pH units. Soda ash raises TA too. If your TA is already high, aeration can raise pH without adding alkalinity. Retest before another dose.

Example: 10,000 gal, pH from 7.0 to 7.2 in the first step, total alkalinity 100 ppm as CaCO₃, CYA 0 ppm: 18.32 oz by weight.

Alkalinity

lb NaHCO₃ = ΔTA ppm as CaCO₃ × gallons × 8.34 ÷ 1,000,000 × (84.007 ÷ 50.045)

The estimate assumes pure sodium bicarbonate. A mole of it supplies one alkalinity equivalent; a calcium-carbonate equivalent is half its molar mass. The formula uses that conversion to turn the gap in your TA readings into a weight of baking soda.

Example: 1,000 gal, a 10 ppm total alkalinity increase measured as CaCO₃: 0.14 lb.

CYA

lb = ΔCYA ppm × gallons × 8.34 ÷ (1,000,000 × purity fraction); oz by weight = lb × 16

The formula assumes granular CYA at 98% purity (0.98). You’ll see a first addition of 60% of the full estimate. Wait at least seven days, or longer if the label or test instructions require it, then measure CYA and calculate the next addition from that reading.

Example: 1,000 gal, a 5 ppm CYA increase, granular CYA at 98% purity; full estimated correction: 0.04255 lb.

Calcium hardness

lb CaCl₂ product = ΔCH ppm as CaCO₃ × gallons × 8.34 ÷ 1,000,000 × (110.98 ÷ 100.09) ÷ CaCl₂ fraction

Take calcium chloride purity from your product label: 77% and 94% enter the formula as 0.77 and 0.94. The dose fills the gap between your hardness reading and target. To assess calcium-carbonate saturation, include the rest of your water balance. Get a separate assessment for metal-corrosion concerns.

Example: 10,000 gal, a 10 ppm calcium hardness increase measured as CaCO₃, calcium chloride at 77% purity: 1.201 lb.

Volume and equipment

Multiply your pool’s volume in cubic feet by 7.48 gal/ft³ to get US gallons. The kidney formula gives a rough estimate. For an L-shaped pool, split the arms at their shared edge so you count each part once. Turnover flow is gallons ÷ (hours × 60); daily runtime is turnovers × gallons ÷ (GPM × 60). If the result exceeds 24 hours, you need more flow to fit that schedule into a day. Annual electricity cost is watts ÷ 1,000 × hours/day × 365 × price/kWh, assuming you run the pump every day. To compare savings, use measured flow and power for the alternative. Before choosing a pump, compare your system curve with that model’s curve at the RPM you’ll use.