Pool Water Balance

In Tech Talk by Steve Donohoe2 Comments

What is balanced pool water?

Balanced water is when calcium carbonate does not precipitate out of the water and stick to the plaster, plumbing, heater and ev

erything else in its path; which is called, “scaling.”  And at the same time, balanced pool water does not corrode and dissolve the plaster, m

ortar, or metal with which it comes in contact – this is called, “corrosive.”  Balanced pool water is neither scaling nor corrosive.

When pool water has been scaling for some time, the pool walls will feel very rough (like sand paper) due to the calcium carbonate sticking to the plaster.  Calcium will also build up in the heater, making it less efficient, and will clog the plumbing, thereby reducing circulation.

When a pool has held aggressive or corrosive water, the walls will be eroded (or feel pitted).   The metal in the heater (iron and copper) will erode into the pool water and cause brown, or a turquoise blue staining of the plaster.

To be balanced, the pool water needs just the right amount of calcium carbonate.

In 1936, Wilfred Langelier developed a method for predicting whether water will precipitate, dissolve, or be in equilibrium with calcium carbonate.  This method, the “Langelier Saturation Index” (LSI) is widely used in the pool industry today to determine balanced water.

pH, Total Alkalinity (TA), Calcium Hardness, Total Dissolved Solids (TDS) and Temperature are all part of the index.  In our CPO class, we use the worksheet on the left when learning about the LSI and how to use it.  We also discuss the fact that cyanuric acid (CYA) is part of Total Alkalinity.  If the CYA is over 60ppm, its contribution to TA interferes with the index, so it must be subtracted out.  The common practice is to divide the CYA reading by 3, and then subtract the quotient from the TA reading.

Keep your water Balanced — protect your  pool and equipment!


Thanks to all folks at PoolCorp – SCP Riverside, for hosting our CPO class this past Thursday and Friday, April 26-27.  And a special thanks to Chris for helping us carry all our equipment and supplies upstairs!


  1. Steve,
    Thanks for the emails and the info. Not only is it helpful but I bet it’s also good for your business. Hope everything is going well. God Bless and keep in touch.


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