LaMotte Pool & Spa Owner's Handbook - Manual (Page 11)

pH
Water Balance - Protecting the Pool or Spa
pH is the measure of the acidity of the water. The pH scale extends from
0 to 14 with 7 being neutral. As the pH moves lower than 7.0, the water
becomes more acidic and tends to be corrosive; as pH moves up higher
than 7.0, the water becomes less acidic (or more basic) and could lead to a
scale forming condition.
Since most water has the tendency to either corrode or leave small, crusty
“scale” deposits, it is important to properly balance the factors of pH, total
alkalinity and hardness. Depending on where you live, the water can
contain a variety of minerals. These minerals directly affect whether the
water will corrode, scale or be in balance. In addition to pH, total
alkalinity and calcium hardness, temperature plays a role in water balance
and must be considered when determining ideal levels in pools or spas.
The reason is because in warmer water a substance called calcium
carbonate tends to fall out of solution more rapidly, thus leaving behind
scale deposits. For example, in 60°F (16°C) pool water, a good practice
would be to keep the pH level closer to 7.6 if the alkalinity and hardness
are in the ideal range. In 80°F (27°C) pool water, a pH of 7.3 would be
best. A professional pool and spa retailer can provide a “saturation index”
calculation to target your ideal pH level.
Note: a high pH level (above 7.8), will inhibit the ability of free chlorine
to sanitize water efficiently. If your water source has a high pH, the form of
chlorine selected can actually help to lower the pH. (For example: If your
water source is a pH of 8.2 you may wish to use Trichlor since it has a pH
of 3.0). For several reasons, including bather comfort, the ideal pH of pool
or spa water is 7.2 - 7.6.
When using the 5-way strip, read pad 4 to determine pH. Keep your results
in the orange, ideal range, colors. If the color turns yellow, add pH
increaser as shown in the charts at the end of this book. If the pH is not up
to the ideal range within 24 hours, add more pH increaser or consult
a local pool professional (the pH could be far below pH 6.8 and in need of
serious attention). If the pad turns red, add pH decreaser to bring the pH
down into the ideal range. The same process should be followed if the pH
remains high after you have added pH decreaser, continue to add more or
consult a professional. Note: if the pH test pad ever turns purple it means
the chlorine or bromine level is well above 10 ppm. Bathers should not
enter the water until the chlorine or bromine level is below 10 ppm.
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