Pool Calculations and Formulas Flashcards

A pool water test shows a Langelier Saturation Index (LSI) of -0.6. What does this value indicate?

Answer: The water is corrosive and may damage surfaces and equipment

A negative LSI indicates corrosive (aggressive) water that can etch plaster and corrode metal; the acceptable range is -0.3 to +0.3.

Using the PHSI formula LSI = pH + TF + CF + AF − 12.1, calculate the LSI for a pool with pH=7.6, Temperature Factor=0.6, Calcium Factor=1.8, and Alkalinity Factor=2.0.

Answer: -0.1

LSI = 7.6 + 0.6 + 1.8 + 2.0 − 12.1 = 14.0 − 12.1 = −0.1, which falls within the acceptable balanced range.

What is the recommended total alkalinity range for most swimming pools?

Answer: 80–120 ppm

Total alkalinity should be maintained between 80–120 ppm to provide adequate pH buffering without causing pH lock.

Which chemical is used to RAISE total alkalinity with only a modest effect on pH?

Answer: Sodium bicarbonate (baking soda)

Sodium bicarbonate (NaHCO₃) raises total alkalinity while having only a minor effect on pH, unlike soda ash which raises pH significantly.

The recommended calcium hardness range for a concrete or plaster swimming pool is:

Answer: 200–400 ppm

Calcium hardness for plaster and concrete pools should be maintained at 200–400 ppm to prevent both scaling and etching.

When calcium hardness drops below 150 ppm, what is the most likely consequence for a plaster pool?

Answer: Etching and pitting of plaster surfaces

Water with low calcium hardness is aggressive and will leach calcium from plaster surfaces, causing visible etching and pitting.

Which chemical is added to pool water specifically to RAISE calcium hardness?

Answer: Calcium chloride

Calcium chloride (CaCl₂) is the standard granular product used to increase calcium hardness in pool water.