Swimming Pool Blog

Swimming Pool pH - Who Cares?

Pool pH and Alkalinity - Close Cousins!
by Rob Cox, October 17, 2011

Swimming Pool pH - Who Cares?

total alkalinity and pH chart for pools


Pool pH - a measurement of the relative acidity or basicity of your pool water.

Who Cares?!?

Well, your pool surfaces care a whole lot. Low pH and Alkalinity can lead to etched plaster finishes or a vinyl liner that becomes less like vinyl and more like plastic. Plastic fittings on returns or skimmer faceplates can also become more brittle and the shiny chrome finish on pool lights and ladders can become oxidized or chip off.

Swimmers too, prefer a pH in the range of 7.2 - 7.5. Everything in nature has a pH level, you've heard of pH balanced shampoo? And is it any coincidence that the pH of the human eye is 7.35?

Chlorine sanitizers also prefer a lower ph range, and lose a great amount of efficacy at pH levels above 7.6. By 8.0, only a small portion of your chlorine tablet is actually doing any good. High pH makes chlorine very tired and lazy.

Keeping your pH level in range also inhibits algae growth. Most aquatic organism find a slightly higher pH preferable to a more acidic, corrosive water pH, and pool algae loves a high pH level.


pH is defined by Wikipedia as a negative decimal logarithm of the hydrogen ion activity in a solution.


pH in your swimming pool is an approximation of the amount of activity of Hydrogen present in your pool water, for example. Although pool pH is not an exact measurement of hydrogen - you could still be somewhat correct if you said that pH stands for the power of Hydrogen.

Essentially, pH is a scale of how acidic or basic your pool water is. At a pH value of 7.0, the water is considered neutral, neither acidic or basic. As the pH level rises, each point up or down the scale is 100x more acidic or more basic. That is, 8.5 is a hundred times more basic than 7.5. This is why the pH is referred to as a logarithmic scale; each decimal point movement is 10x more or less than it's neighbors above and below.ph chart for pools


So, what's this mean for the pool owner? 

Test your pool water with a quality test kit. The better pool test kits will also have some reagents called Acid Demand and Base Demand. These additional tests tell you exactly how much acid or base to add to your pool. Starting with your regular pH test sample, if the pH is high, add the Acid Demand reagent, dropwise (one drop at a time), until the color changes to a desired pH level. Then refer to a chart, where you cross reference the number of gallons in your pool by the number of drops you added until the color changed.

The chart will tell you exactly how much pH decreaser to add, and has charts for both liquid muriatic acid, or granular sodium bisulfate. The Base Demand test works exactly the same way, only it's used when your pH level is too high, and you want to know how much base to add. If you don't have a test kit that includes Acid Demand and Base Demand reagents, add small adjustment amounts, allow to circulate for 8 hours, and then test again.

So, remember that proper pH will lead to longer lasting pool surfaces, more effective chlorine and happier swimmers. Keep an eye on the pH level, and make quick adjustments with an on-hand stock of pH decreaser and pH increaser.