How to Test the pH of a Swimming Pool

Keeping our swimming pool water balanced is our number one priority.  Balanced water is healthy water.  It makes the pool look inviting.  It keeps our pool’s surface and our equipment safe.  Most importantly, it keeps swimmers from getting a water borne disease or even just discomfort.  We test for many different things we perform a test at home.  If you take a water sample to your local swimming pool supply store, they most likely test for even more things.  One of those, and an important one, is the pH of the pool water.

What is pH?

pH stands for “potens hydrogen”.  This is the potential (or power) of hydrogen.  This is actually a scale used to determine how acidic or how basic something aqueous is.  In this case, our pool water.  If a body of water has a higher concentration of H+ (hydrogen) ions are considered to have lower pH values than basic (alkaline) water.  

High pH

If you test your pool water and have a high pH, your water could be considered “basic” or “scale forming”.  This renders sanitizers less effective.  This can expedite scale formation around the edges of your pool, in your plumbing and equipment.  Pools that are sanitized with liquid chlorine or utilize a salt system tend to have a higher pH.  When our pH is high, we will want to bring it down using either sodium bisulphate (dry acid) or muriatic acid (liquid acid).  Make sure you check your alkalinity as well before adjusting the pH.  A low alkalinity reading can cause your pH level to become unstable and “bounce” around.  The ideal range for swimming pool water’s pH is between 7.2-7.8.  Although 7.4 is the money spot.  This is where the sanitizer is most effective.  It is also the level our body’s pH is, so the water will feel more comfortable to swimmers.

Low pH

If you get a low pH reading when you test your water is more on the acidic side.  This often means your alkalinity is low as well.  If you need to raise both the pH and the alkalinity, I recommend sodium bicarbonate (alkalinity up).  Since the pH and alkalinity work on a sort of “buddy system” they tend to go low together.  This is not always the case.  Sometimes we may find our alkalinity to be in range (between 80-120 ), but have a low pH.  In this case, I would suggest using sodium carbonate (soda ash) to raise the pH to the desired levels.  When swimming pool water is considered “acidic” it can wreak havoc on your swimming pool surface and be corrosive to your plumbing and your equipment.  It will also be irritating to swimmers.

Test Strips

One method of testing your swimming pool’s pH is by using test strips.  These often test for four or more fields, with pH being one of them.  I suggest purchasing test strips that also check for alkalinity too so you know if your pH reading is stable.  With a test strip, you dip the strip into a sample of your pool’s water, wait the designated time on the test strip’s label, and compare it to the chart that comes with the test kits.  Oftentimes, you will find this chart on the back of the bottle of test strips itself.  Compare the color of the pH field to the color range provided on the chart.  Whatever color the little square is closest to is you pH range.  Notice I said “range”.  Since colors can be more open to interpretation, you will most likely not be able to pinpoint your exact pH.  You may not be able to tell if it is a 7.4 or a 7.5, but the important thing is that you will know if it is high or low. 

Test Kits

Test kits can come in many sizes.  By “sizes” I mean the amount of different fields they test for.  They have very simple ones that just check for chlorine and pH to the advanced ones a pool professional would use which can test for just about everything.  These kits use little numbered bottles known as reagents.  By adding a particular amount and combination of certain reagents, one can test for things like pH.  They come with a decanter or vial that you would add the reagents to your pool water in.  Add the reagent, always following the test kit’s instructions, and compare the color to the color strip next to it.  Again, since it is using colors, the results can be open to interpretation.  But I find test kits to be slightly more accurate and precise than test strips.  Don’t forget to test your alkalinity as well!

Spin Labs

There is new technology in the swimming pool world known as a photometer.  Much like comparing the colors on the previous tests I mentioned, these machines utilize a color comparison to determine certain levels.  The water is injected with a syringe into a spin disc and then placed in the machine.  The machine spins it around for approximately 1 minute and then uses the color to transmit a reading onto either a computer screen or a device, depending of the software you have.  You will see these in a lot of swimming pool supply stores.  They are available for purchase for home use as well.  You  will need to make sure the machine is always calibrated or it could skew your results.  Over or under filling the disc will also give you an inaccurate reading of pH and whatever else you are testing for.  This is a more expensive way to test as you have to not only buy or rent the machine and software, but you have to buy the dicks, which can be anywhere from .50c to $2.00, depending on how you buy them.

Well, there you have it.  We now understand what pH is, why it is important, why we need to know the level and how to adjust, if needed.  See you poolside!