LaMotte Pool Manager Water Quality Handbook - Manual (Page 22)

Total Dissolved Solids (TDS)
What is TDS?
Total dissolved solids refer to the amount of dissolved
substances or minerals (actually charged ions) within
the pool. These substances enter the pool either through
the original water supply or by the addition of treatment
chemicals. As water evaporates total dissolved solids
remain behind and increase over time. Distilled water is
a solution that contains no dissolved solids. Sea water,
on the other hand, contains a vast amount of total
dissolved solids.
Due to evaporation and intense chemical treatments,
dissolved solids should be closely monitored in spas.
Why do we test TDS?
Water with high TDS readings may be cloudy and cause
corrosion. Total dissolved solids should be kept under
2000 parts per million. If TDS exceeds this amount, part
of the pool water should be drained and replaced with
fresh (low TDS) water.
How do we test TDS?
Most public pools do not have on-site equipment for
analyzing total dissolved solids, and a water sample must
be taken to a local pool supply retailer who has a TDS
meter. A TDS meter measures the electrical
conductivity of a water sample. An electrical current is
passed between a two-part electrode and the meter then
displays the total dissolved solids level. The dissolved
minerals in water conduct electricity and a total
dissolved solids probe or instrument can be effectively
used to measure TDS in parts per million.
Ideal Range for TDS
Less than 2000 ppm. As a general rule TDS should not
increase 1500 ppm above the initial start-up amount.
Note: salt chlorine pools will run higher.
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