LaMotte Pool & Spa Owner's Handbook - Manual (Page 5)

Additional reasons to routinely test your water:
In addition to the obvious goal of determining what treatment chemicals
are needed to protect the bather and the pool there are many other good
reasons to test the water.
How much treatment chemical to add - By testing the water
and using the treatment tables found in the back of this book (or on the
chemical product label), the analyst can closely predict how much
treatment chemicals are needed. This testing avoids a costly overdose of
chemicals that can create larger problems than the original one.
Total Alkalinity - To avoid undesirable changes in the pH level the
alkalinity must be maintained in the ideal range (near 100 ppm). Total
alkalinity helps to stabilize the pH of the water so that chemical
treatments or environmental conditions will not rapidly raise or lower the
pH to a damaging level. Such changes can also occur after adding large
doses of chlorine, since one form of chlorine may have a very low pH
while another a very high pH. If the pH of your source water is high or
low, consult with a pool professional to select a type
of chlorine or sanitizer that makes sense for
your water and the environmental conditions.
Total Chlorine - If the total chlorine level
ever exceeds the free chlorine level,
a superchlorination or shock treatment
is needed. High total chlorine levels
indicate that undesirable ammonia
or nitrogen compounds have
“combined” with the free chlorine to
make the sanitizer much less active and
create odor and swimmer irritation.
Total Hardness - When a hardness
level is too low, it can cause corrosion.
If it is too high, it can settle or “drop out”
of solution as chalky white or tan colored
deposits on component surfaces.
These deposits, often referred to as
“scale,” could eventually lead to clogged
pipes, or damaged motors, heaters,
and filters.
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