Enter the total alkalinity, desired total alkalinity, and volume of the pool into the calculator to estimate the acid required to reduce total alkalinity (assumes 31.45% muriatic acid (HCl) and alkalinity reported as ppm/mg/L as CaCO₃).
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Acid Demand Formula
The following formula is used to estimate the volume of 31.45% muriatic acid (HCl) required to reduce total alkalinity from TA to DTA (with alkalinity expressed as ppm/mg/L as CaCO₃).
AD = (TA - DTA) \cdot V \,/\, 500000
Variables:
- AD is the acid demand (liters of 31.45% muriatic acid)
- TA is the current total alkalinity of the pool water (ppm or mg/L as CaCO₃)
- DTA is the desired total alkalinity (ppm or mg/L as CaCO₃)
- V is the volume of the pool water (liters)
To estimate the acid demand, subtract the desired total alkalinity from the current total alkalinity. Multiply the result by the volume of the pool, then divide by 500,000. The result is an approximate volume of 31.45% muriatic acid needed to reduce total alkalinity by that amount.
What is an Acid Demand?
Acid demand is a measure of how much acid is required to reach a desired target in a solution. In water treatment and swimming pool maintenance, “acid demand” often refers to the amount of acid needed to lower pH to a target value (commonly estimated with an acid-demand test). On this page, the calculator uses the term acid demand to mean the approximate volume of 31.45% muriatic acid (HCl) needed to reduce total alkalinity from TA to DTA.
How to Calculate Acid Demand?
The following steps outline how to calculate the Acid Demand (AD).
- First, determine the total alkalinity of the pool water (TA) in ppm (mg/L as CaCO₃).
- Next, determine the desired total alkalinity (DTA) in ppm (mg/L as CaCO₃).
- Next, determine the volume of the pool (V) in liters.
- Next, gather the formula from above = AD = (TA – DTA) × V / 500000 (assumes 31.45% muriatic acid / HCl).
- Finally, calculate the Acid Demand (AD).
- After inserting the variables and calculating the result, check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
TA: total alkalinity of the pool water (ppm) = 150
DTA: desired total alkalinity (ppm) = 100
V: volume of the pool (liters) = 5000. Using the formula above: AD = (150 − 100) × 5000 / 500000 = 0.5 liters of 31.45% muriatic acid.
