**1.** Take a water sample from the pool.

**2.** Add sodium bicarb (baking soda) to the pool. Add enough bicarb to make a measurable change (this will be about 2-4 pounds per 10,000 gallons). Make sure you weigh or measure the chemical and try to add exactly 2, 3 or 4 pounds. Write down how much chemical you added.

**3.** Wait long enough for the chemical to be completely dispersed and blended throughout the entire pool. (This will vary from minutes to even hours depending on method of addition and circulation.

**4.** Take a second water sample from the pool.

**5.** Test the total alkalinity of the two samples. For sufficient accuracy, use a test method that is accurate to within 1 or 2 ppm. For example, if your test kit uses 1 drop of titrant for each 10 ppm of total alkalinity, use a sample volume that is 10 times the sample size. Then each drop of reagent or titrant used is 1 ppm instead of 10 ppm.

**6.** The Formula Factor for sodium bicarb is 71,400.

**7.** Apply the following formula using the formula factor for bicarb:

(71,400) × (Amount of bicarb added to pool in lbs – 2, 3 or 4 lbs) / ppm change = Pool Volume

**Example:**

You add 4 pounds of sodium bicarbonate to the pool. The starting total alkalinity was 110 ppm and the ending total alkalinity was 115 ppm.

(71,400 ) (4) / 115 – 100 = 19,040 gallons

AUTHOR: Robert Lowry

www.honestpoolchemistry.com