English Instructor Manual (PDF) - Metric Version - National ...

Key Points: Discuss the various aspects of total dissolved solids (TDS). These include:
TDS is the measure of all minerals dissolved in water. TDS is easier to understand
if it is renamed as “totally dissolved solids”. For example, sugar is a solid before it is
dissolved in water. But once dissolved, it becomes “totally” dissolved and can no longer
be observed in the water. However, if enough sugar is continuously dissolved, the water
becomes saturated and will not dissolve anything else. This is called “old” water.
Generally agreed that TDS should not become higher than 1,500 mg/L above its start up
value.
The only inexpensive way to reduce TDS is by draining or diluting the existing water with
water with a lower TDS level.
TDS levels up to 1,000 mg/L use a saturation index factor of -12.1 when calculating the
Saturation Index. For TDS greater than 1,000 mg/L use -12.2.
Key Points: Discuss that the Langelier saturation index is a method to measure if water is
balanced. Explain that it is not the only method, but that it is the most commonly used method in
the pool industry.
Using the Langelier Saturation Index handout, explain how to use the formula for
calculating saturation index. Explain how to use the charts for converting measured
values for total alkalinity, calcium hardness, and temperature into factors that can be
used in the formula.
Explain that when all the factors are calculated, the following values can be used to
determine if the water is corrosive, scale-forming, or balanced:
The ideal range for balanced water is between -0.3 to +0.3.
Activity: Using the Langelier Saturation Index handout, the Saturation Index Worksheet, and the
Water Quality Guidelines handout, do several saturation index calculations. Provide students with
blank copies of the Saturation Index Worksheet to use for this lesson and to have for the fi nal
exam.
Explain that when making corrections for unbalanced water, follow these rules:
All the values must be in the ideal range. For example, if the pH is 7.9 in the original
calculation, it must be changed to a value between 7.4-7.6 when making corrections to
balance the water.
The SI value must be in the ideal range (-0.3 to +0.3). Even though all the water
balance elements may have values in the ideal range, the SI may not be ideal. If this is
the case, changes should be made to the saturation index values for pH, total alkalinity,
and calcium hardness so that the SI falls within the ideal range.
Key Points: Explain that the difference between the original measured values and the theoretical
values that the participants have used to balance the water is called the adjustment. For example,
if the total alkalinity was 50 mg/L in the original calculation and was changed to 80 mg/L to
balance the water, the adjustment for total alkalinity is 30 mg/L (80 - 50 = 30). To balance this
water in reality, an amount of chemical that will increase the total alkalinity by 30 mg/L will have to
be added to the water. That calculation will be explained later.
Key Points: Discuss the adjustment order. Typically, the alkalinity should be adjusted before pH.
If calcium hardness needs to be lowered, do that before making other adjustments since the water
will need to be changed or diluted.
© 2014 National Swimming Pool Foundation® Page 59