Methodology & Formulas

Every result on PoolCareCalc comes from a standard, published pool-chemistry relationship. We state them all here so you can check our work. These are estimates: real water chemistry varies, so always test and add chemicals gradually.

Pool volume

Volume = surface area × average depth × 7.48 US gallons per cubic foot. Average depth is (shallow + deep) / 2. Surface area is length × width (rectangle), πr² (round), or π × (L/2) × (W/2) (oval ellipse).

Chlorine & shock dosing

The anchor: raising free chlorine by 1 ppm (1 mg/L) in 10,000 US gallons (37,854 L) requires 37,854 mg ≈ 37.85 g of pure available chlorine. For any product we divide by its available-chlorine fraction:

• Cal-hypo 65% and 73%; dichlor 56%; trichlor 90% (dry weight).
• Liquid chlorine 12.5% (density ~1.168 g/mL), 10% (~1.14), household bleach 6% (~1.09) — converted from weight to volume using density.

Routine free chlorine target: 1–3 ppm. Shock (breakpoint) target: about 10 ppm; algae recovery needs more. Trichlor and dichlor also raise cyanuric acid over time.

pH, alkalinity, cyanuric acid, calcium

• Total alkalinity (raise): ~1.5 lb baking soda per 10,000 gal per 10 ppm.
• Total alkalinity (lower): ~25.6 fl oz muriatic acid (31.45%) per 10,000 gal per 10 ppm.
• pH (raise): ~6 oz soda ash per 10,000 gal per ~0.2 units.
• pH (lower): ~12 fl oz muriatic acid (31.45%) per 10,000 gal per ~0.2 units at typical alkalinity.
• Cyanuric acid (raise): ~0.81 lb stabilizer per 10,000 gal per 10 ppm.
• Calcium hardness (raise): ~1.25 lb calcium chloride (100%) per 10,000 gal per 10 ppm; 77% flake needs proportionally more.

pH response depends strongly on total alkalinity, so pH figures are approximate — dose in stages and re-test. Cyanuric acid and calcium hardness can only be reduced by dilution.

Pump & filter sizing

Required flow (GPM) = volume ÷ (turnover hours × 60), targeting one turnover in ~8 hours for residential pools. Minimum cartridge area = flow ÷ 0.375 GPM per sq ft; D.E. and sand are shown at their typical design flow rates. Actual pump selection also depends on plumbing size and head loss.

Filter-cartridge cross-reference

Model numbers, square footage, fitment, and the Pleatco / Unicel / Filbur equivalents are compiled from manufacturer and aftermarket published cross-reference charts. Dimensions are nominal and vary slightly between brands; always confirm against your existing cartridge before ordering. We only list real, currently-sold models and leave any field we cannot confirm blank rather than guess.

Questions about a formula? See the about page or the disclaimer.