Posted by: rolande | April 21, 2013

Tracking your Pool’s Water Quality History

taylor-test-kitsWhen you have a pool, one of the many fun jobs is tracking the quality of the pool water to insure the pH is in the right range and the chlorine isn’t too high or too low. However, these are the basic, superficial measurements. Beyond these typical measurements, though, it is just as important to know that your water won’t scale or eat away at the pool’s surface over time. When I was a teenager, it was my job to track the pH and chlorine in our pool. Back then, I never realized or fully appreciated the importance of the overall chemistry of the water. The calcium hardness and alkalinity and temperature play a big part in that equation, in conjunction with the pH. Now that I am much older and have a lot more invested in my own pool, I want to be sure that I am monitoring the right indicators and have a history of it so I can see the effects over time and how particular treatments impact the water.

I have created a Pool Water Quality History Google spreadsheet as a template that anyone can use to record and graph their own water quality over time. One of the key indicators I wanted to capture automatically was the Langelier Saturation Index. The LSI is a calculated number used to predict the calcium carbonate stability of water. It indicates whether the water will precipitate, dissolve, or be in equilibrium with calcium carbonate. It was developed in 1936, by Wilfred Langelier, as a method for predicting the pH at which water is saturated in calcium carbonate (called pHs). The LSI is expressed as the difference between the actual system pH and the saturation pH. This Index value is a pretty telltale indicator of the overall water quality. As long as you can maintain this value between -0.5 and +0.5, you are in good shape. This spreadsheet automatically calculates the individual Factors that make up the LSI, as well as the LSI value itself. It also includes several graphs to track the values over time and some additional advice on balancing your pH. The key is to not let the pool supply company talk you into chasing your pH around with chemicals. Remember that they are in business to sell you more chemicals. That doesn’t mean that you don’t need chemicals like Muriatic Acid or Soda Ash. You just need to know how and when to use them and not just use them because the pool company told you to.

I had found that there were a quite a few options out there to manually calculate the Saturation Index, at a point in time, based upon the typical water quality measurements. But, I’ve found that it is much more helpful to have a log of this info over time, if you are really serious about tracking the overall quality and identifying what treatments work best in your situation. Everyone’s pool and water quality are different. There is no single magic formula to find water balance. I researched and found the formulas to calculate the Factors of the LSI Index. I’ve incorporated them into this spreadsheet and verified them myself over the past several months of data that I’ve collected. I have found this approach pretty useful for managing the water in my own pool. I hope that you will find this just as useful.

I would love to hear feedback from anyone who finds this spreadsheet useful or has suggestions to improve upon it. Pool season is just about upon us. I hope that everyone enjoys the summer swimming in their pools.




  1. This is very impressive. However I’m from Australia, our units are Metric and I have a Salt Water pool.

    Can you provide some advice on how to change the units and change this spreadsheet to deal with a Salt Water pool ?


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