Turn the filter off. An accurate reading is attained when the water is still.
Open the testing strip bottle and remove one strip. Follow the product's specific instructions, but most require you to dip the strip in the water for a few seconds and remove it. Place the strip on a flat dry surface and wait the amount of time indicated on the product before determining the pH level.
Compare the test strip with the color chart included on the bottle of testing strips. Waiting the correct amount of time to read the strip is critical to accurate readings. Do not wait too long, as the color may fade on the strip.