Carl, I know that many people have not bought into the Langelier Saturation Index, but there is a bit of science behind it and it is not just used by the pool industry. Water treatment pants have been using it for years to prevent scaling in the water system. Yes, if you keep your numbers in recommend range, the LSI is fairly close to zero so you do not have to worry about it. However, sometimes pool owners have to work with high calcium hardness levels which LSI can help target proper alk and PH so that scaling will not occur. LSI gives me piece of mind knowing I went the extra mile to make sure my numbers are right.

Here are a few links if you are interested:

http://www.lenntech.com/langelier-index-eng.htm
http://www.awt.org/members/publicati...l/Fall1991.htm
There are many more you can get with google.