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SPN OCT 2011 WaterTesting BALANCED WATER
The Langelier Index is a way of determining how much calcium is in your pool water. If it is not controlled it leads to deposits in the pool structure and pipe works
B
alanced Water (or the Langelier Index) is an important factor in keeping your pool up-to-standard.
When water is in balance, it is said to be neither corrosive nor scale-forming. In other words, it will neither dissolve an existing layer of scale nor will it deposit a layer of calcium scale. Unbalanced water can aggressively eat away at the pool’s infrastructure.
For most well run pools, the water should be in balance if the pH value is kept within the recommended range. However, there are other factors that can have a significant effect on the condition of the water.
Monitoring the alkalinity and maintaining its concentration helps to keep a constant level of pH within the pool water. High alkalinity levels reduce the effectiveness of adding acid or alkali to the water, so pH levels are more difficult to change. Low alkalinity levels increase the effectiveness of acid or alkali. This means tiny additions of chemical can radically change the pH, making it difficult to manage. Stable alkalinity and pH levels help the effectiveness of disinfectant used in the pool, so it is important to monitor and maintain levels regularly.
Changes in calcium hardness levels can affect fixtures and fittings within the pool. Low levels often result in the loss of grout around the tiles, as the water tries to satisfy its need for calcium. High levels are not necessarily a problem, as long as the water remains balanced. However uncontrolled build up of calcium in the water can lead to deposits in the pool structure and pipe works. This can reduce the efficiency of the plant, filters, dosing systems and lead to increased maintenance, labour costs and time.
Ideally a slightly positive Balanced Water result should be aimed for. This will leave a thin layer of calcium deposits on the pipework, which can act as protection against corrosion. High calcium levels can also affect other tests carried out including the DPD test. In areas of hard water it may be necessary to use a DPD High Calcium Tablet to reduce the interference during measurement.
LANGELIER SATURATION INDEX (LSI) The Langelier Saturation Index (sometimes also known as the Langelier Stability Index) was developed in the 1930’s to determine a formula resulting in a single calculated number which is used to notify how much calcium is in the water. The golden result of just above ‘0’ means the water is ‘in balance’.
The Langelier Saturation Index is simple and reliable. It uses various parameters that can have an effect on the water balance and each is given a factor to give an Index value. Those parameters are: pH; total alkalinity; calcium hardness; total dissolved solid; temperature.
Each of these parameters has an effect on each other as proven by the formula below. However, generally speaking, low measurements result in negative balanced water, high measurements result in positive balanced water.
- Balance = Corrosive+ Balance = Scale Forming Low pH
High pH Low Alkalinity Low Temperature High Alkalinity
Low Calcium Hardness High Calcium Hardness Low TDS
High TDS Low Temperature
To calculate the Langelier Index more accurately,
THE ANSWER TO THE ABOVE TEST
each reading is given a factor which is put into the following formula:
pH + Temperature factor + Alkalinity factor + Calcium Hardness factor - TDS factor
To calculate the respective Factor for each measurement, the table at the bottom left of this page may be consulted.
EXAMPLE CALCULATION pH 7.2
+ Alkalinity 15
7.2 (taken from reading – no factor conversion required) Factor 1.1
+ Calcium Hardness 15 Factor 0.7 + Temperature 29 = Sum
- TDS 2000 = Langelier Index
Factor 0.7 9.7
Factor 12.2 -2.5
TRY IT FOR YOURSELF WITH THIS TEST!
Imagine you have taken the following readings from the sample of your pool water. By using the factor conversions and formula on this page, can you work out the Langelier Index of the pool and whether or not the water is in balance?
• pH 7.35 • Alkalinity 105 • Calcium Hardness 400 • Temperature 29.5 • TDS 1440
-2.5 would represent quite an aggressively corrosive state of water, resulting in galvanic attack.
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pH 7.35 + Alkalinity 105
= 7.35 = Factor 2.0
+ Calcium Hardness 400 = Factor 2.2 + Temperature 29.5 = Factor 0.7 Sum
= 12.25 - TDS 1450 Balanced Water
= Factor 12.15 = 0.1
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