Tips for selecting an appropriate pH meter
The most accurate way to measure pH
For accurate results, you will want to use a pH probe and meter setup. Paper pH strips or kits where you compare water color to a chart after adding a reagent do not provide accurate results for Portland's water. The Hach Pocket Pro is a basic yet reliable option for people who want to test their water pH at home. Our field technicians use the Hach HQ40d multimeter with an Intellical PHC281 refillable pH electrode.
How to adjust your testing for Portland's water
Compare to our system pH. Portland's water is currently treated to be at a pH of 8.8. The pH of Portland's water can vary by a small amount in the distribution system, but it generally ranges from about 8.0 and 9.0. If your pH readings are well outside of this range, recalibrate your pH meter according to the manufacturer's directions or replace your probes.
Use a probe designed for water with low ionic strength. The Bull Run Watershed is our main water source. Due to its low dissolved mineral content, water from Portland's Bull Run source has what is called "low ionic strength." In water with low ionic strength, it's difficult to accurately measure pH. Using a pH probe designed specifically for low ionic strength water will help.
Be aware that temperature can affect your readings. The temperature of Portland's water typically varies between 38 and 75 degrees Fahrenheit. Temperature can affect pH measurement. As temperature goes up, pH goes down, and as temperature does down, pH goes up. Some pH meters include Automatic Temperature Compensation probes to help you measure pH at any temperature.
Calibrating your pH meter
If your pH meter came with standards or buffer solutions, make sure you replace them before their expiration date.
Follow the pH meter manufacturer's recommended calibration methods. Typical tips are to:
- Use fresh buffer solutions when calibrating the pH probe.
- Perform a calibration verification check using known pH standard solutions. Our technicians use three known solutions when verifying pH: 4.01, 7.00, and 10.01. They then use a solution with a pH of 7.38 to verify that the probes are calibrated correctly.
- Before calibrating, clean the pH probes using deionized water.
- Rinse the containers used to test the known buffer solutions.
Regularly calibrate your pH probe to appropriate reference standards. Our technicians perform three-point calibrations twice each day.
Storing and replacing pH probes
Caring for your pH probes will help you get accurate readings.
- If you have a "wet bulb"-type probe, make sure the probe is properly maintained by using manufacturer-recommended filling and storage solutions. Do not store your probe in distilled or deionized water.
- Replace your pH probe(s) according to the manufacturer's recommendations.
Troubleshooting pH measurements
- Ensure that the pH probe is properly submerged to the indicated line/reference junction.
- Do not use the same pH probe to measure the pH of your raw water feed that you use to measure other liquids; this can cause fouling of the probe and affect the accuracy of your measurements.
- Use unexpired pH probes; otherwise you may end up with inaccurate results.
- Rinse the pH probes to avoid rubbing the sensitive surface, or use a lint-free paper towel to blot the probe.
- Check your batteries. Low batteries in the meter can affect pH readings.
- Follow all other manufacturer procedures.
Aquarium pH and water quality
If you have aquatic animals, it's important to use accurate pH measurements when you adjust their water. Because pH is measured in a logarithmic scale, a change in the pH scale of 1.0 means that there is a tenfold increase in hydrogen activity. Because of the broad range of water quality needs for aquatic species, we recommend consulting with an aquarium professional or specialized reference guide when caring for aquatic animals. One common guide is the 1992 Marine Aquarium Reference, Systems and Invertebrates (ISBN 0-939960-05-2).