Calculators

pH Down

Adjustment inputs

Total alkalinity is treated as ppm as CaCO3.

Pool volume gal Product Current pH Target pH Water temperature Total alkalinity ppm Cyanuric acid ppm Label active ingredient % Liquid density lb/gal Display unit

Product note

Select the acid product from the label.

Prefilled calculator link

Verify before applying a dose

Verify the reading, pool volume, and product concentration against the label. Follow label and site directions; for large corrections, dose in stages, circulate, and retest before adding more.

Estimated addition -

Enter readings to estimate a pH decrease.

Read the pH Down guide.

Estimated pH -

Estimated TA -

TA decrease -

Product basis -

How PoolKit estimates pH Down

PoolKit estimates acid demand by modeling carbonate alkalinity, cyanurate alkalinity, water temperature, and the selected acid product. The dose lowers modeled total alkalinity until the carbonate/cyanurate balance reaches the target pH.

The estimate assumes full mixing, no immediate CO2 exchange with air, no borates or phosphates, and product strength matching the label inputs. It is a planning estimate, not a replacement for staged dosing and retesting.

Sources: PubChem hydrochloric acid, PubChem sodium bisulfate, PubChem cyanuric acid, acid neutralization stoichiometry, and carbonate/cyanurate acid-base equilibrium.

Relationship to alkalinity

Every acid addition lowers total alkalinity. If the pH target requires a large alkalinity decrease, the better site plan may include staged acid/aeration work rather than one full addition.

Field use

Add acid in portions, circulate, and retest pH and total alkalinity before continuing. Label directions, site procedures, and local requirements take priority over calculator output.

When pH needs to move up instead, use the pH Up calculator.

Step	Formula	Value Used
Pool volume	`gallons x 3.785411784`	-
Temperature conversion	`(F - 32) x 5 / 9`	-
Acid product	`formula, molar mass, acid equivalents`	-
Label active ingredient	`active ingredient percent / 100`	-
Liquid density	`product weight / product volume`	-
Current total alkalinity	`test reading as CaCO3`	-
CYA alkalinity	`estimated from pH and CYA chemistry`	-
Current carbonate alkalinity	`TA - CYA alkalinity - water alkalinity`	-
Starting carbonate carbon	`carbonate alkalinity / carbonate alpha`	-
Target total alkalinity	`solve TA at target pH with same carbonate carbon`	-
Acid demand	`current TA - target TA`	-
Product dose	`acid equivalent dose / active fraction`	-
Estimated pH	`solve TA = carbonate + CYA + OH - H`	-
Estimated total alkalinity	`current TA - acid demand`	-

Liquid acid dose depends on both label strength and product density. Change density when the SDS or label gives a better value.

If pH is high because of rapid CO2 loss or aeration, pH may drift again after acid addition.