![]() ![]() The Langelier Index is used to determine the tendencies of water toward corrosion or scaling based upon the pH (potential of hydrogen) of calcium carbonate (CaCO3). (Note: While the cited SI range is commonly taught, the trend now in the pool/spa industry is to recommend a more restrictive range of -0.3 to 0.5 or even -0.3 to 0.3.) No chemical adjustment is necessary if the SI is within ☐.5 units of zero however, conditions producing a value greater than 0.5 may lead to cloudiness and scaling, while conditions producing a value less than -0.5 may cause corrosion of concrete or metal surfaces. SI = pH + TF + logCH + logALK – CONSTANT, where:ĪLK = measured alkalinity minus cyanurate alkalinityĬONSTANT = combined factor for temperature and ionic strength correction, and concentration conversionsĪn SI value of zero means water is properly balanced. It is calculated using the formula shown below. The Langelier Saturation Index, often called the “LSI,” the “saturation index,” or the “stability index,” is a numerical value indicating whether or not water is balanced. About 40 years ago this calculation was adjusted and amended to suit swimming pool water conditions and made into a calculation that determines whether the water is neutral, balanced or unbalanced ( corrosive or scale forming ) ![]() Such a thin layer of scale would protect the cast iron pipes from corrosion. In the 1930`s, Professor Wilfred F.Langelier was commissioned to discover how to lay down a thin layer of scale on the distribution piping of a Large City. ![]()
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