Calculation Assumptions
Purpose
Pool chemistry calculators produce estimates based on the inputs provided and a set of documented assumptions. This page explains those assumptions so users can understand when results may be less accurate for their specific pool.
Ideal Conditions Assumed
All calculators assume: (1) well-mixed pool water — chemicals are uniformly distributed; (2) accurate test results — input values are correctly measured with calibrated equipment; (3) standard water density — 8.34 lbs/gal at approximately 77°F/25°C; (4) pure products at stated concentration — product labels are accurate and products have not degraded.
Expected Inputs
Calculators accept current measured values (e.g., current FC, pH, TA) and target values. Inputs are assumed to reflect the pool water at time of testing. Results apply to the entire pool volume. Inputs should be from a recent test — results from tests taken more than 24 hours prior may not reflect current conditions.
Common Limitations
Calculator results may be less accurate when: (1) pool water is not well-circulated before testing; (2) fill water chemistry differs significantly from neutral; (3) multiple chemicals are being adjusted simultaneously; (4) pool has recently been shocked and equilibration is incomplete; (5) bather load significantly changes chemistry between test and treatment.
Approximations
Dosage calculations use average product concentrations (e.g., 10% for liquid chlorine). Actual product concentration varies by brand, batch, and age. pH adjustment calculations use simplified linear models that are most accurate within ±0.5 pH units of the target. LSI calculations use lookup table interpolation rather than full thermodynamic equations.
Why Calculators Provide Estimates
Pool chemistry involves continuous dynamic processes: evaporation, bather load, temperature fluctuation, UV exposure, and chemical degradation all affect water chemistry between treatments. A calculator provides the best estimate for current conditions, but real-world results depend on factors that cannot be fully captured in any calculation. Always verify results with a follow-up water test 4–8 hours after treatment.
What to Do If Results Seem Wrong
If calculator results appear inconsistent with your experience: (1) verify your input values are accurate; (2) check your test kit reagents are not expired; (3) consult the Known Limitations page; (4) consider that pool-specific factors (surface type, fill water, equipment) may require adjustment. For commercial pools, always consult a licensed pool operator.