pH and Your Pool


Definition:  pH is the logarithmic measure of the acidity or alkalinity of a solution where 7 is neutral and lower numbers indicate increasing acidity (increased hydrogen ion concentration) and higher numbers indicate increasing alkalinity (decreased hydrogen ion concentration)

pH = -log10[H+]

  1. Keep pool water slightly alkaline with a pH of 7.2-7.6.

  2. Pool water that is out of range (either high or low) in pH causes damage to surfaces such as plaster, fiberglass, and liners, as well as damage to plumbing lines and pool equipment.  Water that is lower than 7.2 or higher than 7.6 also is uncomfortable for swimmers causing irritation to skin, eyes, and ears.  Out of range pH can also negatively affect chlorine’s ability to sanitize the pool.

  3. Being slightly out of range is worse than it sounds.  The pH scale is logarithmic, meaning that any increase or decrease by whole numbers represents a ten-fold change in acidity or alkalinity.  For example:  8.0 is ten times as alkaline as 7.0, and 9.0 is one hundred times more alkaline than 7.0.  This is true for the other end of the scale as well:  4.0 is one thousand times more acidic than 7.0.  

  4. Check water chemistry frequently.  pH can be altered by a wide variety of factors including but not limited to swimmers, rain, chemical usage, and debris.

  5. Use muriatic acid to lower the pH in plaster and fiberglass pools.  Use powdered pH decreaser (sodium bisulfate) to lower pH in vinyl liner pools.  To increase the pH in all types of pools use powdered pH increaser (sodium carbonate).

  6. Newly surfaced plaster pools will consistently have an increasing pH level.  The new surface is highly alkaline in nature and as it cures the surface will cause the pool water to become more alkaline.  For newly surfaced plaster pools, Hawaiian Pools and Landscaping recommends testing the pH level daily and adjusting as necessary.

  7. Salt pools also consistently have an increasing pH level.  These types of pools will need to be monitored more frequently and likely adjusted more frequently.

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