A pH meter measures the acidity or alkalinity of water using a standard pH scale. Acidic water is soft, while alkaline water is hard. A pH meter is more accurate than chemical tests and comes with calibration liquids. It is commonly used in water quality monitoring and by aquarists to prevent fish disease or death.
A pH meter is a hand-held device that tests water for its level of acidity versus base, or alkalinity. If the water is equally acidic and alkaline, it is recorded as neutral on the meter. The pH meter uses a standard pH scale to measure 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 ranges from 0 to 6.9, with 7.0 being neutral. Because 7.0 is neutral, 6.8 is considered only slightly acidic. Likewise, 7.2 is only slightly alkaline, with the base scale going to 10.0 or higher. In general, acidic water is soft while alkaline or basic water is hard.
In the absence of a pH meter, water is tested for pH by adding chemicals to a water sample. Depending on the agents used, a bright yellow result could indicate very acidic water; blue, neutral; and dark brown, alkaline water. Keys are interpreted as positions along the scale.
Liquid pH tests can be messy and require some guesswork when it comes to reading. In contrast, a pH meter is a digital device with a glass electrode probe attached. The probe is inserted into the water to be tested and the pH of the water is digitally displayed. It takes seconds and is much more accurate, assuming the meter has been calibrated correctly.
While 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 basic (10.01).
Calibration is done by testing liquids with the probe and adjusting the meter readings. A pH meter should be recalibrated monthly for best results. When not in use, the probe tip should be stored in an acidic solution. If the probe dries out, it will need to be replaced.
Water quality monitors commonly use pH meters. Other types of meters test for solids such as soil or even foods. Many aquarists use pH meters instead of liquid tests. The probe can be permanently placed 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, fluctuating pH can cause disease or death to fish, so monitoring pH closely is crucial.
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