Langlier Saturation Index. Are you having trouble balancing your pool?


Langlier Saturation Index

Maintaining good water balance will ensure trouble free operation, prevent scale build up and extend plate life. Some Enviroswim users experience small amounts of scale from the Oxidiser plates appearing in their pools (only an aesthetic issue) or in extreme cases excessive scale build up on their plates requiring manual cleaning Most users do not experience this and the self cleaning plates usually have very little scale build up.

The difference in these situations is the pool water balance across all of the balance elements. The most volatile pool balance parameter is pH. It is also one of the easiest to adjust. Maintaining pH only is not enough to prevent scale formation.The Enviroswim operating manual outlines the recommended values for water balance parameters. These are generally expressed as ranges such as pH in the range 7.1-7.5. These balancing chemicals interact in total with each other to establish an overall balance which is referred to as either scale forming or corrosive. Some of the balance elements are very stable and others such as pH are very volatile. As things are expressed in ranges – if all elements are present at the top end of their ranges it is likely that you will have a scale forming environment. If you are experiencing excessive scale buildup on your plates or having small flakes of scale from the plates appearing in your pool it is likely that your pool has a balance that is scale forming.

The Langlier Saturation Index (LSI) is a method for determining the scale forming potential of the water. Some pool shops will calculate this index for you and some understand its use, otherwise there are on-line calculators such as: and now some smartphone apps.

The LSI should be kept slightly negative to prevent scaling.

The parameters that are used in a complete LSI calculation are

 pH

 Calcium Hardness


 Alkalinity

 Temperature

As a rule the higher the value for an element the higher the saturation index calculated and a high value for one element may be offset by a low value for another element.

The recommended range for the index is from -0.5 to 0.0 – i.e. slightly negative. The entire range provides acceptable LSI values as it is only at values outside of the range -0.5 to 0.5 that action would usually be taken.

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