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pH Meter Buying Guide

- Dec 18, 2017 -

pH meters can be used in the garden, for the pool, or in a laboratory to test the level of acidity or alkalinity that is present in a substance. A typical pH meter can accurately measure and display the pH reading of a liquid, solution, or semi-solid substance.

pH Levels

pH stands for potential of Hydrogen. Determining the pH level in a liquid or solution depends on the presence of hydronium ion in relation to hydroxide.

The pH scale is based on the presence of either acids or bases in a substance. Acids have more positively charged hydrogen ions and include substances like lemon juice and vinegar. Bases, or substances with alkaline molecules, contain more negatively charged hydroxide ions as found in ammonia and milk of magnesia.

The scale ranges from zero to 14 to indicate whether the substance is acidic or basic. A pH level of 7 represents a neutral balance, which is a substance that is neither acidic nor basic. For example, pure water has an equal number of hydronium ions and hydroxide; therefore, it is neutral and has a pH level of 7. For every whole number from 7, the pH level of the substance is 10 times more or less acidic or basic than the next value. Substances containing pH levels less than 7 are acidic while levels greater than 7 are basic.

pH Level


0Battery acid
1Hydrochloric acid
2Lemon juice
3Orange juice
4Tomato juice
5Black coffee
7Pure water
9Baking soda
10Milk of Magnesium
12Soapy water
14Liquid drain cleaner


The pH meter has two basic parts - a special measuring probe, which is connected to an electronic voltmeter. The probe contains two electrodes that measure hydrogen ion activity. The glass electrode has a glass bulb at the tip that acts as a pH-responsive electrode. A second electrode, known as the reference electrode, contains either a mercury-mercurous chloride, potassium chloride, or a silver-silver chloride. The reference electrode has a neutral pH balance against which the pH level of the substance is measured.

The electrodes may be contained in separate probes or in a single probe. Some smaller models have single probes that are the size of a pen. The meter can be a moving-coil meter that resembles a weight scale or a digital meter with numeric display.

Once the instrument is submerged in a solution, the two electrodes act as a battery that produces an electric charge. A small voltage of roughly 0.06 volt per pH unit from the attached voltmeter will measure the difference between the two electrodes. This process is called the ion exchange as the ions in the instrument and the substance are swapped. A large difference in voltage between the electrodes and the substance indicates a large difference in hydrogen ion activity.

Calibration and Maintenance

For accuracy in measurement, the pH meter must be calibrated before use. This can be done by adjusting the temperature of the pH meter. Some meters have built-in thermometers that automatically adjust to corresponding changes in temperature. Another method of calibration is by dipping the meter into buffer solutions of known pH levels to adjust the meter.

To calibrate in test buffer solutions, the pH probe should be rinsed with distilled water before placing into a pH 7 buffer solution. Allow the probe to be submerged for 30 seconds, and then adjust the meter to pH 7. Some models have a calibration button that may be pressed to adjust the meter. After a second rinse in distilled water, place the probe into a pH 4 buffer solution and readjust the meter to pH 4. Rinse the probe and remove any excess liquid before use. Be sure not to reuse and to discard any test buffer solution to avoid contamination.

After using the pH meter, the instrument should be stored in a pH 4 solution or other storage solution. It is recommended to soak the probe in distilled water once per month if not used regularly.

Uses for pH Meters

Unusual uses for pH meters include wine-making, cheese-making, and stain removal. For example, the crisp, tart taste in some wines is based on the level of acidity present. The general pH balance of acidity in table wines is considered to be between 3.3 and 3.7. In order for cheese to ripen and develop in flavor and texture, it must be within a narrow pH range. The ideal pH level for mozzarella cheese, for example, is 5.3. Finally, a flat surface pH meter can measure the pH levels of fabric and carpet to help determine the best cleaning solution for stain removal.

The electronic device is most commonly used in gardening, pool maintenance, and aquarium water testing.


Nutrients in plant soil depend on a proper pH balance. Depending on the specific plant type, the soil needs to contain either more or less acid or alkaline. Soil pH meters test pH levels for plants such as flowers and fruits. Some testers have one or two probes with replaceable electrodes to be placed directly into the ground. Other models are handheld and allow gardeners to test smaller samples on a dish or spoon contained within the device itself. Several soil samples should be tested in different areas of a garden to ensure accuracy of the pH reading.

Pool and Spa Maintenance

Pool chemicals in swimming pool or spa water should be regularly tested for their pH levels for the safety of the swimmers. Swimming pool or spa pH meters test the water quality by measuring the chlorine level. It is recommended to test the pool chemicals after backwashing the pool filter for the most accurate reading. Chlorine levels should be tested at least once per week while monthly tests can be conducted for total alkalinity, calcium hardness, total dissolved solids, and stabilizers. Since the pH of human eyes is at 7.2, the ideal pH level for swimming pool water is between 7.0 and 7.6.

A pool or spa that is too acidic, or has a low pH level, can cause a number of problems. The surface of a pool made of plaster or grouted tile will dissolve. Metal parts such as pump connections and pipe fittings will also corrode. Chlorine used to disinfect the pool will not effectively sanitize the swimming pool water. Swimmers will experience dry and itchy skin, burning in the eyes and nose, and fading of their swimwear.

A pool or spa containing too much alkaline, or a high pH level, is equally problematic. The swimming pool water may turn cloudy or murky due to calcification. The sand filter in a pool may turn into cement and will no longer trap dirt that may enter the pool. As with an acidic pool, swimmers will also experience dry and itchy skin and burning in the eyes and nose.


The water in an aquarium requires a delicate pH balance to prolong fish and marine plant life. Aquarium pH meters can be used to test the water once a month. Testing marine aquaria is important as some aquatic organisms thrive in certain pH levels. This is especially critical when a fish becomes ill or has deceased as a slight change of 0.2 in pH levels can harm aquarium fish.

The optimal pH range varies by tank, water, and fish and marine plants within the tank. Although there is no set pH level, there is typically an ideal range. While natural seawater has a pH level of 8.0 to 8.3, a reef aquarium could be kept at a pH level of 7.8 to 8.0, and some freshwater fish could live in water with a pH range of 6.5 to 7.5.

Depending on the fish and marine plants to be added, an aquarium may be filled with hard or soft tap water. Consult with the seller regarding the correct pH levels before adding water to an aquarium tank. Hard tap water typically has a high pH because it contains a large amount of mineral content. A reverse osmosis unit or pH decreaser will remove minerals from tap water. Alternatively, soft tap water may need to have the pH level raised by adding minerals.

Another concern is the level of carbonate hardness in aquarium water. Carbonate hardness, or kH, indicates the water's ability to neutralize acids without altering pH levels. A high level of kH is more likely to stabilize the pH levels in the aquarium. kH kits to test the level of carbonate hardness are often combined with pH testing kits. Test the pH levels frequently for an imbalance in pH levels before adding or removing minerals from the aquarium water.

To test the pH level of water before adding to an aquarium, test it separately in a bucket or other container. For accuracy, allow the water to adjust overnight or add an air stone to oxygenate the water before testing. Test the water within the first 24 hour period and again after 48 hours. If there are not any major changes to the pH levels, the water can be added to the aquarium. If any issues are apparent after testing, leave several buckets of water with an air stone in each for 48 hours to allow the water to adjust to its actual pH level before adding to the aquarium.

Finding pH Meters on eBay

To purchase a pH meter, begin at the eBay home page. Since pH meters can be used for multiple purposes, they can be found in various categories. Begin from All Categories on the main page.

Meters used for gardening can be found in the Home & Garden subcategory. From the drop-down menu, select Yard, Garden & Outdoor Living, and then choose Gardening Supplies. Next, select Garden Tools & Equipment and click on Moisture & pH Meters.

To test water in aquaria, pools, or spas, pH meters can be found within the Home & Garden subcategory as well under Tools. Select Meters, Testers & Probes from the drop-down menu and search for "pH meter" in the search toolbar. Narrow down results by using the filters on the left-hand side of the results page by condition, price, location, Auction or Buy It Now options.


pH meters are versatile tools for testing the acidity or alkalinity in a number of water sources, including aquaria, pools, and spas. The instrument can also check the pH measurement in soil for optimal levels for gardening. Frequently testing the pH level will ensure safe levels for the home and garden.

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