Langelier Index 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 CaCO3) AF = alkalinity factor, log (alkalinity, ppm as CaCO3) To calculate the exact Langelier Index of your water please use the WATER INDEX reference tables. 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 parameters must be measured; calcium hardness, alkalinity and pH. Find the hardness and alkalinity factor in the reference tables below. The water temperature is, in general, maintained between 24°C (76°F) and 34°C (94°F). Assuming the temperature is kept within those ranges, an average value or 0.7 may be used. Water balance = pH+TF+HF+AF Water Index Reference Table Water Balance Condition Recommendation 11.0-12.0 Corrosive Increase pH and/or alkalinity 12.1-12.3 Acceptable Balance Retest water frequently 12.4-12.6 Ideal Balance Maintain 12.7-12.9 Acceptable Balance Retest water frequently 13.0-14.0 Scale Forming Reduce pH and/or alkalinity Temperature Calcium Hardness Alkalinity °C °F TF mg/L (as CaCO²) HF mg/L (as CaCO²) AF 0 32 0 5 0.7 5 0.7 4 39 0.1 25 1.4 25 1.4 8 46 0.2 50 1.7 50 1.7 12 54 0.3 75 1.9 75 1.9 16 60 0.4 100 2.0 100 2.0 20 68 0.5 150 2.2 150 2.2 24 75 0.6 200 2.3 200 2.3 28 82 0.7 250 2.4 250 2.4 32 90 0.7 300 2.5 300 2.5 36 97 0.8 400 2.6 400 2.6 40 104 0.9 500 2.7 500 2.7 50 122 1.0 1000 3.0 1000 3.0 10 Photometers 10.57 www.hannainst.com | benchtop
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