Methodology & Formula Sources

Chemical mass calculations use unit conversions and stoichiometry. The pH model is a closed-system equilibrium estimate, not a laboratory validation of your pool. Confirm volume, fresh measurements, formulation and label instructions. All later additions require fresh readings.

Salt

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

Sodium chloride mass. Select salt target and limits from the exact cell manual.

Example: 10,000 gal, salt 2,800 → 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)

For 65% available chlorine, use fraction 0.65, not ingredient purity 0.68. Divide ounces by 16 for pounds.

Example: 10,000 gal, FC increase 1 ppm, 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)

Trade percent is grams available chlorine per 100 mL. Here 10 means 10%, not 0.10. Household bleach labels give sodium hypochlorite weight percent; converting requires density and the Cl₂/NaOCl molar-mass ratio. Ingredient weight percent is not trade percent.

Example: 10,000 gal, FC increase 1 ppm, 10% trade available chlorine: 12.79 fl oz.

pH down

acid equivalents = (initial alkalinity − modeled alkalinity at the next pH) × water volume in litres

Closed carbonate/cyanurate equilibrium at 25°C, with measured TA corrected for cyanurate and water contributions to infer dissolved carbon. HCl equivalents convert using its weight percent and density; sodium bisulfate uses molar mass and purity. One step is at most 0.2 pH; aeration, temperature and unmeasured buffers can change field response.

Example: 10,000 gal, pH 8.0 → first step 7.8, measured TA 100, CYA 0, 31.45% w/w HCl: 3.709 fl oz.

pH up

Solve carbonate/cyanurate equilibrium including 1 mole dissolved carbon and 2 equivalents alkalinity per mole of Na₂CO₃ added

Soda ash is not a fixed ounces-per-pH-change rate. Use measured TA and CYA; one step is at most 0.2 pH. Aeration can raise pH without increasing TA when TA is already high. The model assumes pure sodium carbonate.

Example: 10,000 gal, pH 7.0 → first step 7.2, measured TA 100, CYA 0: 18.32 oz by weight.

Alkalinity

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

One mole of bicarbonate supplies one equivalent; a CaCO₃ equivalent is half its molar mass. Assumes pure sodium bicarbonate.

Example: 1,000 gal, TA increase 10 ppm as CaCO₃: 0.14 lb.

CYA

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

Granular cyanuric acid purity 98% means fraction 0.98. The calculator starts with 60%, then waits seven days and recalculates from a fresh reading.

Example: 1,000 gal, CYA increase 5 ppm, 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

Use the product’s actual CaCl₂ content (e.g. 0.77 or 0.94). The chosen hardness target does not by itself establish saturation balance or metal-corrosion risk.

Example: 10,000 gal, CH increase 10 ppm, 77% CaCl₂: 1.201 lb.

Volume and equipment

Geometry uses 7.48 US gal/ft³. Kidney volume is an estimate; L-shaped arms must not overlap. Turnover flow is gallons ÷ (hours × 60); runtime is turnovers × gallons ÷ (GPM × 60). Schedules over 24 hours are infeasible. Annual electricity is watts ÷ 1,000 × hours/day × 365 × price/kWh. Savings require a measured alternative flow and power scenario. Pump selection needs an actual system curve and a named model/RPM curve.