Hanna Instruments HI 83266 - Manual (Page 4)

6 7
Alkalinity
Alkalinity is the measure of the total concentration of alkaline substances, mostly bicarbonates, dissolved in the
water. The higher the alkalinity the more resistant the water is to pH change, the alkalinity
buffers the water.
At the same time, high alkaline water is a major contributor to scaling problems like incrustation in filtration
equipment, pumps, and piping.
It is recommended to maintain the alkalinity value within the range from 80 to 125 ppm as calcium carbonate (CaCO
3
).
pH
The pH of the water is an important factor since at lower pH the corrosion rate increases. If the alkalinity values
are sufficiently high it will not be difficult to control the pH. Most pools managers do prefer to keep the pH
between 7.2 and 7.4, that does ensure low corrosion rates and a sufficient activity of chlorine.
Langelier Index (LI)
The Langelier Index is a powerful tool to calculate the water balance, and to predict corrosion or scaling problems.
Theoretically, a LI of zero indicates perfect water condition for swimming pools. If LI>0, scaling and staining of the water
is present, and if LI<0 the water is corrosive and highly irritating. A tolerance of ±0.4 is normally acceptable.
The Langelier formula is expressed as:
LI = pH + TF + HF + AF – 12.5
where:
LI = Langelier Index (also called Saturation Index)
pH = pH of the water
TF = temperature factor
HF = hardness factor, log(Ca Hardness, ppm as CaCO
3
)
AF = alkalinity factor, log(Alkalinity, ppm as CaCO
3
)
To calculate the exact Langelier Index of your water please use the WATER INDEX reference tables at the end of
this chapter to find the Temperature, Hardness and Alkalinity factors.
Recommendations
For most pools, water is balanced if:
• The pH value is maintained within the recommended ranges of pH 7.2 - 7.6
• Ideally the Alkalinity should be maintained within a range of 80 - 125 ppm
• The Calcium Hardness should be maintained within a range of 200 - 400 ppm.
To calculate your water balance three tests are required, measure the Calcium Hardness, the Alkalinity and the
pH of the pool water. Find the Hardness and Alkalinity Factor in the WATER INDEX reference tables below.
The water temperature is in general controlled between 24
o C (76 o F) and 34 o C (94 o F) to ensure pleasant bather comfort. The
Temperature Factor in this temperature range has minor importance; therefore an average value of 0.7 may be used.....
Calcium Hardness
The presence of calcium in the system is desired to ensure filming on those places where the temperature is relatively
high, like in boilers and pipes transporting warm water. Scaling must be avoided because it reduces heat transfer
and pump capacity. Beside the calcium carbonate deposits in the pipes, high scaling values do cause cloudy water.
It is recommended to maintain the calcium hardness value within the range from 200 to 400 ppm as calcium
carbonate (CaCO
3
).
A simple calculation classifies your water in corrosive, scaling, acceptable or ideal balanced, with treatment recommendations:
Water Balance = pH + TF + HF + AF
WATER INDEX REFERENCE TABLES
EXAMPLE:
Water Balance = pH + TF + HF + AF = 7.2 + 0.7 + 2.4 + 1.9 = 12.2
Conclusion: the water is acceptable balanced but there is some risk that the water becomes corrosive;
frequently testing is recommended.
Recommendation
Increase pH and/or Alkalinity
Retest water frequently
Retest water frequently
Reduce pH and/or alkalinity
Water Balance
11.0 – 12.0
12.1 – 12.3
12.4 – 12.6
12.7 – 12.9
13.0 – 14.0
Condition of Water
Corrosive
Acceptable Balance
Ideal Balance
Acceptable Balance
Scale forming
°C
0
4
8
12
16
20
24
28
32
36
40
50
°F
32
39
46
54
60
68
75
82
90
97
104
122
TF
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.7
0.8
0.9
1.0
mg/L
(as CaCO
3
)
5
25
50
75
100
150
200
250
300
400
500
1000
HF
0.7
1.4
1.7
1.9
2.0
2.2
2.3
2.4
2.5
2.6
2.7
3.0
mg/L
(as CaCO
3
)
5
25
50
75
100
150
200
250
300
400
500
1000
AF
0.7
1.4
1.7
1.9
2.0
2.2
2.3
2.4
2.5
2.6
2.7
3.0
Temperature Calcium Hardness Alkalinity
Pool water conditions
Temperature 30°C
pH 7.2
Alkalinity 80 mg/L
Hardness 230 mg/L
Factor value
(nearest values)
TF = 0.7
pH = 7.2
AF = 1.9
HF = 2.4