How to Calibrate and Use a pH Water Testing Meter

9/14/20 - Zoro Staff

Acidity in water is measured using what’s known as pH levels. Whether you’re an environmentalist investigating a potentially polluted stream, a chemist working in a lab, or a pet owner with a prized collection of tropical fish, a pH testing meter is a useful and accurate tool for determining water quality based on the pH level, or the amount of acids or alkalis present.

The Science of Measuring pH Levels

In scientific terms, the pH value of water is found by comparing the ratio of hydrogen ions (H+) and hydroxyl ions (OH-). Ions are atoms with either too many or too few electrons present. Acids dissolve in water and form positively charged hydrogen ions (stronger acids form more hydrogen ions than weak acids). An alkali, or base, forms negatively charged hydroxyl ions (and, again, stronger alkalis form more ions than weaker versions). 

The pH levels in water act similar to a battery and a pH meter measures the voltage, or electrical potential, within a solution much like a voltmeter measures electricity. A pH water testing meter compares the voltage in a water sample and compares it with a sample with known voltage. The difference between the two is the pH level.

The range of pH levels goes from 0 to 14. A level of 7 is considered neutral. Water with more free hydrogen ions is more acidic, and water with more free hydroxyl ions is less acidic, or “basic.” A pH water testing meter will indicate the degree of activity of either an acid or a base by measuring this ionic activity.

For example:

• If there is a higher concentration of hydrogen than hydroxyl, the substance is acidic and it will register a pH level of less than 7. 
• Conversely, if there is a higher concentration of hydroxyl than hydrogen, the substance is basic and will have a pH value greater than 7.
• Equal amounts of both ions mean the tested material is neutral and it will show a pH value of 7.

Measuring pH levels is important because it indicates the amount of chemicals, heavy metals, and nutrients found in water. It also shows whether a particular body of water is safe for marine life to use. For comparison, normal rainwater has a pH of between 5 and 6—it does feature some acid due to the carbon dioxide gas found in the atmosphere—whereas ammonia has a pH of between 10 and 11.

Using the Water Testing Meter

Step 1: Warm up and electrode cleaning

Before using a pH water testing meter, you need to prepare any testing materials and give it 30 or so minutes to warm up. Then, you need to clean the electrode. Remove it from its storage solution and give it a rinse with distilled water under an empty waste beaker.

Step 2: Calibration

Your pH testing meter should be calibrated before every use because, over time, these machines can drift from their accurate settings. To calibrate the meter, which resets the readings of the device to ensure maximum accuracy, you’ll use two buffer samples, which are specially prepared (and usually colored) solutions that are guaranteed to contain a specific pH level. 

One should be neutral, with a pH of 7. The other should be close to the expected sample. 

The meter includes a membrane that allows hydrogen ions (H+) to pass through, creating a voltage. Put the electrode in the neutral buffer and press the “measure” button to calibrate. Be careful handling the electrodes, as they feature delicate parts that are expensive to replace. Once the reading is stable, set the pH meter on the touchpad to the buffer sample’s reading again (it should register exactly or very close to 7) by pressing the measure button again.

Remove the electrode and then give it a rinse with distilled water and dry it gently with a lint-free cloth or tissue. Then, put the electrode into the sample buffer and push the button so it begins its measurement. Once the reading has stabilized, set the pH meter to the buffer pH, and press the button once more. Rinse the buffer again before use.

Step 3: Using the meter

Your pH water testing meter is now calibrated and ready to go. Put the electrode into the sample tub and press the button. It will take a few minutes to complete its measurement.

Wait for the reading to stabilize and press the measure button again to determine the pH level of the sample. 

Finally, rinse your electrode again and store your meter once the device dries off.

Measurements

Both high and low pH levels can have a negative impact on water quality. A high pH may be responsible for bitter-tasting water and the formation of mineral deposits around pipes and appliances. High pH also can negate the effectiveness of chlorine, resulting in the need to add more chlorine to sufficiently disinfect drinking water or swimming pools.

On the other end of the spectrum, very low pH water can corrode and damage metal pipes and results in metallic tasting water. 

When used properly, a pH testing meter can help you determine if water is at high or low pH levels so you can take the necessary action to make it safe for any number of important uses.

Product Compliance and Suitability

The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.