Base demand & ph adjustment – LaMotte DPC-52 Water Testing Laboratory User Manual
Page 15
BASE DEMAND & pH ADJUSTMENT
In certain cases it may be necessary to monitor and adjust the alkalinity and/or pH of the
pool water to a higher level for a better balance of chemical characteristics. Titration of a
pool water sample with a standard base reagent to pH 7.4 provides a factor for corrective
adjustment with soda ash or equivalent base chemical.
NOTE: For accurate results in pools with low pH and high alkalinity readings, the
alkalinity level must be adjusted to the proper range before performing the Base Demand
test.
PROCEDURE
1. If the pH sample is yellow to orange, there is a base demand. Hold the tube flat
against the pH coloruler (3164), parallel to the center channel, with the two
standard colors on the right. Grasp the comparator tab and test tube between thumb
and index finger, and hold toward a window or light. Use the glass pipet (0371) to
add Base Reagent (WL-6460), one drop at a time, to the tube. Swirl the tube several
times after each drop. Count the drops and continue titrating until the color
matches the pH 7.4 standard color.
2. Use the number of drops added and the base demand table below, to determine the
amount of Soda Ash (Sodium Carbonate, Na
2
CO
3
) required to adjust pool or spa
water to an optimum pH of 7.4.
SODA ASH REQUIREMENT
Pool or Spa
Volume in
Gallons
Number Of Drops Of Base Titrant Added
1
2
3
4
5
6
7
8
9
10
100
0.0
0.1
0.1
0.1
0.2
0.2
0.2
0.3
0.3
0.4
250
0.1
0.2
0.3
0.4
0.5
0.5
0.6
0.7
0.8
0.9
500
0.2
0.4
0.5
0.7
1.1
1.1
1.2
1.4
1.6
1.8
1,000
0.0
0.1
0.1
0.1
0.2
0.2
0.2
0.3
0.3
0.4
2,500
0.9
1.8
2.7
3.5
5.3
5.3
6.2
7.1
8.0
8.8
5,000
1.8
3.5
5.3
7.1
10.6 10.6 12.4 14.1
1.0
1.1
10,000
3.5
7.1
10.6 14.1
1.3
1.3
1.5
1.8
2.0
2.2
20,000
7.1
14.1
1.3
1.8
2.7
2.7
3.1
3.5
4.0
4.4
25,000
8.8
1.1
1.7
2.2
3.3
3.3
3.9
4.4
5.0
5.5
50,000
1.1
2.2
3.3
4.4
6.6
6.6
7.7
8.8
9.9
11.0
Ounces Soda Ash
Pounds Soda Ash
Example: A rectangular pool measures 20’ x 40’ with an average depth of 5’ and gives a
base demand test result of 8 drops of Base Reagent.
1. Calculate volume of water (see p. 13):
40’ x 20’ x 5’ x 7.5 = 30,000 gallons
2. In the Base Demand Table, read this volume as:
20,000 + 10,000
3. Reading from Table = 3.5 + 1.8 = 5.3 lbs Soda Ash
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