Calculate muriatic acid demand for pool water by entering total alkalinity, desired alkalinity, and pool volume to find acid volume.
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Acid Demand Formula
The acid demand calculation estimates how much 31.45% muriatic acid, also called hydrochloric acid or HCl, is needed to lower total alkalinity in pool water. The calculator uses liters as the base pool volume unit and ppm as CaCO3 as the base alkalinity unit.
Rearranged formulas are used when you leave a different field blank:
- AD = acid demand, in liters of 31.45% muriatic acid
- TA = current total alkalinity, in ppm or mg/L as CaCO3
- DTA = desired total alkalinity, in ppm or mg/L as CaCO3
- V = pool volume, in liters
- 500000 = conversion factor based on alkalinity as CaCO3 and approximately 10 equivalents per liter for 31.45% muriatic acid
If you enter current total alkalinity, desired total alkalinity, and pool volume, the calculator solves for acid demand. If you enter acid demand instead, it can solve for the starting alkalinity, target alkalinity, or pool volume. For dilute pool water, ppm and mg/L are treated as equivalent for total alkalinity.
Typical Pool Alkalinity Ranges
| Pool type or condition | Typical total alkalinity | Result meaning |
|---|---|---|
| Common target range | 80 to 120 ppm | Often used as a general pool balancing range. |
| Low alkalinity | Below 80 ppm | pH may swing more easily. Acid is usually not added to lower alkalinity further. |
| High alkalinity | Above 120 ppm | pH may tend to rise, and acid addition may be used to lower alkalinity. |
Unit Conversions Used
| Measurement | Conversion used |
|---|---|
| 1 US gallon | 3.78541 liters |
| 1 cubic meter | 1000 liters |
| 1 liter | 0.264172 US gallons |
| ppm as CaCO3 | Treated the same as mg/L as CaCO3 |
Example
Example 1: Calculate acid demand
You have a 40,000 liter pool, current total alkalinity of 140 ppm, and desired total alkalinity of 100 ppm.
The estimated acid demand is 3.2 liters of 31.45% muriatic acid.
Example 2: Calculate desired alkalinity after acid addition
You start at 130 ppm total alkalinity, add 2 liters of 31.45% muriatic acid, and the pool volume is 50,000 liters.
The estimated desired or resulting total alkalinity is 110 ppm.
FAQ
What strength of acid does this calculator assume?
It assumes 31.45% muriatic acid, which is a common pool-grade hydrochloric acid strength. If your acid is weaker or stronger, the result will not match exactly. Weaker acid requires more volume, and stronger acid requires less volume.
Can acid lower pH and total alkalinity at the same time?
Yes. Muriatic acid lowers both pH and total alkalinity. This calculator focuses on the alkalinity change, not the final pH. After adding acid and allowing the pool to circulate, you should retest pH and alkalinity before adding more chemicals.
Why must current total alkalinity be higher than desired total alkalinity?
Acid addition is used here to lower alkalinity. If the desired total alkalinity is higher than the current total alkalinity, the calculator cannot compute an acid dose because acid would move the value in the wrong direction.
