Once you have measured the various parameters
below, you can use this convenient Langelier Saturation Index calculator to determine whether
your water is corrosive, scale forming or nicely balanced. If
it is corrosive it will try to saturate itself by dissolving the
structure of your pool. If it is scale forming it will try to
correct its over saturation by precipitating the hard water salts
causing cloudy water and eventually deposit scale on pool components.
Saturation Index = pH
+ CF + AF + TF - 12.1
CF is the Calcium
Hardness factor. Optimum range 75 to 150 mg/litre.
AF is the Total
Alkalinity factor. Optimum range 100 to 150 mg/litre.
TF is the Temperature in Degrees Centigrade. The HSE suggest water
temperature between 27 and 29.5 Deg. C.in commercial pools.
pH. Optimum range 7.2 to 7.6.
If the result of this calculation is zero then the water is
balanced. If the answer is less than 0 then the water will tend
to be corrosive. If it is greater than 0, then it is said to be
scale forming. An acceptable range is -0.5 to +0.5. If the result
is outside this range, adjustments should be made to the hardness,
alkalinity and pH to bring it as close to zero as possible and ideally within the optimum ranges shown above. Be aware however, that whilst the water may be balanced from a corrosion and scaling point of view it does not necessarily mean that it is ideal for sanitiser efficiency and bather comfort.