Definition:
pH (which stands for “potential Hydrogen”) measures acidity. You’ve probably heard of the pH scale, which measures acidity to alkalinity, with neutral substances smack dab in the middle… which is, of course, 7.
Why does pH matter?
pH matters because it affects chlorine, and ultimately, the quality of your water — off-balance pH pretty much throws off your game no matter which end of the scale you end up on.
Here’s a primer on how pH works: the scale goes from 0 to 14, where the closer to zero, the more acidic the substance. You want your pool’s pH to be between 7.2 and 7.4 to play nicely with the chlorine. More on that later!
How to Check the pH Level in Your Pool
The easiest way to check the pH level in your pool is with a test kit or test strips. You’ll test for pH and total alkalinity. Remember that your ideal pH level is between 7.2 and 7.4 — anything higher, and your water is too alkaline. Anything lower and your water is too acidic.
Here’s a video that walks you through the basics of checking with a Taylor test kit:
How often should you check pH?
If you’re checking for free chlorine twice a week during the active swimming season, then that’s plenty. Checking pH should be part of your regular pool maintenance routine. Letting your pool water get too acidic or too alkaline can be a big problem to wrangle — it’s better to test and adjust frequently.
How do chlorine and pH interact?
Think of pH and chlorine as two sound inputs at a rock concert — if you turn up the guitar too high, you can’t hear the vocals anymore. If you blast the vocals, you can’t hear the guitar. Neither makes for a good performance. The pH and chlorine have to be in complete harmony, both at levels appropriate for their intensity.
Let’s cut the metaphor and talk science. Chemically, adding chlorine to water creates free chlorine, the germ-fighting stuff that kills contaminants. The germ-fighting stuff is hypochlorous acid. Acidic water is a good habitat for free chlorine to do its thing and keep your water clean. If your water is less acidic and higher on the alkaline side, hypochlorous acid can’t form. In short, your water stays dirty. This shows up as scaling and murky water.
So the more acid, the better? Not quite. Pools are for humans after all, humans with skin. Acid and skin don’t really mix (neither do acid and plenty of surfaces used in pools). The magic pH number is 7.2 to 7.4 — acidic enough to let chlorine clean up the nasties and gentle enough for people, who clock in with a pH level of 7.2 to 7.8 on average.
What should you do if your pool’s pH is low?
If your pool’s pH is too low, it means your water’s too acidic. You’ll need to add alkali materials to get closer to the basic end of the scale. Two common substances to increase pH are sodium carbonate (better known as soda ash) or sodium bicarbonate (baking soda).
What happens if your pH level is too high?
If your pH level is too high, your water is too basic for your chlorine to do any good. Your water’s probably looking gunky, swimmers might be complaining about itchy skin, and you need to get some acid in there. Depending on your reading, you’ll add dry acid or muriatic acid to get back to a neutral reading.
What causes a high pH level in a pool?
There are several reasons your pH levels may be off the charts. Obviously, adding strong chemicals like chlorine, calcium, or lithium hypochlorite chlorine can make a difference. Sometimes it’s as simple as a week of summer weather heating the water up (your pool heater can do this, too). You can even see a raised pH effect if you’ve recently updated a finish to your pool surface (pebbles or plastic). At the end of the day, it’s not anything you did wrong — over time, pH rises.
Can a high pH level cause my pool to turn green?
Yes, this can be an effect of a high pH level. It may also be a chicken-and-the-egg situation: sometimes algae causes a high pH reading. Either way, add some acid to get back to neutral territory.
The Stuff You Need
We don’t do affiliate links, FYI. Anything we’re recommending is something we’d use to monitor our pools, too. If we start doing affiliate marketing, trust us, we’ll mention it first.
Cheap test kit that checks for pH and total alkalinity:
Taylor K-1003 Safety Plus Swimming Pool Chlorine Bromine pH Alkalinity Test Kit | $19.48
More expensive, and more comprehensive test kit:
Taylor K-2005C Service Complete Pool Test Kit K2005C | $80.60