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Pool Owner’s Guide · Your Water
pH: The Balance Point of Pool Water
by Spectrum Pool Care
pH is a small number that shapes almost everything about how pool water looks and feels. Here’s what it measures, where it came from, and why the ideal range is so narrow.
pH describes how acidic or basic water is, on a scale from 0 to 14. Seven is neutral; lower numbers are acidic, higher numbers are basic. Each step is ten times the one before it, so water at pH 8 is ten times more basic than water at pH 7. That is why a change that looks small on a test strip can make a real difference in the pool.
For a residential pool, the sweet spot is 7.4 – 7.6, with 7.2 – 7.8 as the acceptable range. Human tears sit right around 7.4, which is one reason water in this range feels so comfortable on the eyes.
A Little History
Where “pH” Came From
The scale was invented in 1909 by Søren Sørensen, a Danish chemist at the Carlsberg Laboratory in Copenhagen, the research lab of the famous brewery. He was studying how acidity affected proteins and needed a simple way to write very small numbers. The “H” stands for hydrogen; the “p” is usually read as “potential” or “power.” More than a century later, his shorthand is on every pool test kit.
Why It Matters
What the Right pH Does
Chlorine at full strength
Chlorine is most effective toward the lower end of the ideal range. As pH climbs, more of it shifts into a slower form, and the pool needs more chlorine to do the same work.
Comfortable water
Water near 7.4 feels gentle on eyes and skin. Swimmers notice the difference long before they know the number.
Surfaces and equipment
Balanced pH protects plaster, tile and metal. Water that runs low can wear surfaces and fittings; water that runs high can leave scale.
Clear water
When pH runs high, calcium can come out of the water as fine, milky particles. Keeping pH in range helps the water stay sparkling.
What Moves It
Why pH Drifts
Moving air through water. Waterfalls, spillways, jets and fountains release carbon dioxide, which nudges pH upward.
Salt systems. A salt cell tends to raise pH as it makes chlorine, so salt pools usually need a little acid on a regular rhythm.
New plaster. Fresh plaster raises pH for its first weeks and months as it cures.
Chlorine tablets. The common slow-dissolving tablets are acidic and tend to lower pH over time.
Rain and fresh water. Rain is naturally a little acidic, and top-off water brings its own pH and alkalinity.
pH has a partner: total alkalinity. Alkalinity acts as a buffer that holds pH steady. When alkalinity is in its range of 80 – 120 ppm, pH changes slowly and predictably; when it’s too low, pH can swing from day to day.
From our routes: on weekly service we check pH on every visit and adjust in small steps, balancing alkalinity first so the pH stays where we set it.
