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Chemistry

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What is a pH Meter?

By R. Kayne
Updated: May 21, 2024

A pH meter is a handheld device that tests water for its level of acidity versus base or alkalinity. If water is equally acidic and alkaline, it registers as neutral on the meter. The pH meter utilizes a standard pH scale for measuring these aspects of water quality. The level of concentration of positive hydrogen ions in the water determines the result.

The acidic side of the pH scale runs from 0 to 6.9, with 7.0 being neutral. Because 7.0 is neutral, 6.8 is considered only slightly acidic. Similarly, 7.2 is only slightly alkaline, with the base scale running to 10.0 or higher. Generally speaking, acidic water is soft while alkaline or base water is hard.

Lacking a pH meter, water is pH-tested by adding chemical agents to a water sample. Depending on the agents used, a bright yellow result could indicate highly acidic water; blue, neutral; and deep brown, alkaline water. Hues are interpreted as positions along the scale.

Liquid pH tests can be messy and they do require some guesswork as to the reading. Conversely, a pH meter is a digital device with a connected glass electrode probe. The probe is placed into the water to be tested, and the pH of the water is digitally displayed. It takes mere seconds and is far more accurate, assuming the meter has been properly calibrated.

Though there are many types of pH meters, common varieties will come with calibration liquids called buffer solutions. These solutions are predetermined to be highly acidic (4.01), neutral (7.01), and alkaline or base (10.01).

Calibration is accomplished by testing the liquids with the probe and adjusting the meter’s readings. A pH meter should be recalibrated monthly for best results. When not in use, the tip of the probe must be stored in acidic solution. If the probe dries out, it will need replacement.

Water quality controllers commonly use pH meters. Other types of meters test solids like soil or even foods. Many aquarists use pH meters in lieu of liquid testing. The probe can be placed permanently in an aquarium sump and the meter, mounted inside the aquarium stand or on a nearby wall. Freshwater cichlids and saltwater fish require alkaline water, while African Nile fish thrive in acidic freshwater. In an aquarium, pH fluctuation can cause illness or death to fish, so monitoring pH closely is paramount.

All The Science is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
By anon156353 — On Feb 26, 2011

Why is the glass electrode of the pH meter best stored immersed in a 3M KCl solution?

By accordion — On Feb 22, 2011

I used a pH scale in high school a few times for different experiments. They are actually pretty easy to use, and they can be used in some interesting school-level experiments.

By Leonidas226 — On Feb 17, 2011

Growing up, we used the pH scale to measure the acidity of the poolwater to keep it at a proper level. We didn't want the water too hard, because then it would get dirty, and we also didn't want it to soft, cause then it would break down the natural alkaline substances in the skin and hair, which can be bad for you.

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