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What is pH testing?

One of the most common water quality measurements taken is pH. pH is a measure of how acid or alkaline water is, but this is actually determined by the amount of free hydrogen and hydroxyl ions in the water. Water that has more free hydrogen is acidic, and conversely water that has more free hydroxyl ions is alkaline.

Measuring pH is in the range of 0 – 14: the scale is logarithmic, so each number represents a 10-fold change in pH. For example, water with a pH of 4 is ten times more acidic than water with a pH of 5. Within this range, a pH of 7 is neutral, any pH below 7 is acidic and any pH above 7 is alkaline. To give an example of this in context, normal rainfall has a pH of about 5.6, and a stream would be expected to have a pH in the range of 6 – 8.

It is important to monitor the pH of a water body because it affects aquatic organisms. Different organisms thrive in varying ranges of pH, and can be adversely affected by just a small change. An alteration in normal pH in a water body can be an indication of increased pollution or other environmental factors. This is due to the fact that pH can be affected by chemicals in the water. The solubility and biological availability of the chemical constituents of water are determined by pH.

These chemical constituents may be nutrients, such as phosphorus, nitrogen and carbon, and heavy metals, such as lead, copper and cadmium. The biological availability of nutrients will affect what organisms can survive in that water. Heavy metals are more soluble in water with a lower pH, which tends to make them more toxic to aquatic life – in particular fish.

Overly acid or alkaline water can have negative effects on water usage. For example, highly alkaline waters cause a bitter taste, and mean water pipes and appliances that use water become encrusted with deposits. Hard water (high pH) areas in the UK have issues with limescale deposits building up in kettles, washing machines, etc. Very low pH water will corrode or dissolve metals and other substances.

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Aquaread's pH testing equipment

pH is a standard parameter on every multiparameter probe from Aquaread. pH is measured by a combined pH and ORP electrode, which is easily identifiable as the only electrode that is not black; it has a clear, gel-filled body. Aquaread's pH sensor measures pH with an accuracy of +/- 0.01.

The following Aquaread products include the pH probe as standard:


The AP-2000 is highly portable and allows the measurement of 10 standard parameters, plus the addition of two optional electrodes and a depth sensor.

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Image of AP-2000
Image of AP-5000


The AP-5000 is also designed to be portable, but allows maximum flexibility as you can add up to 4 optional sensors, rather than 2.

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The latest Aquaprobe from Aquaread features groundbreaking technology to allow long term usage during unmanned water testing. This water pH tester has 6 standard parameters and the option to add 6 further ISE or Optical sensors.

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Image of AP-7000

How to use a pH meter

pH testing equipment from Aquaread comes in the form of Aquaprobes, with various electrodes attached to the bottom. One of these measures pH, so that multiple parameters can be monitored simultaneously. To ensure optimum accuracy, pH sensors should be calibrated at least once per week.

To use pH meters, you place the electrode in the water sample. Inside the pH probe supplied by Aquaread there are 2 electrodes that measure voltage (or electrical potential). One electrode is inside a fixed pH sensor liquid, so provides a constant electric potential, the other senses the electrical potential in the water sample.

A pH meter measures the difference between the 2 readings, and then this is translated into pH. The pH measurement will be displayed on the screen of the Aquameter that is used, in combination with the Aquaprobes. The pH electrode must be used and maintained according to the user manual to ensure accuracy and optimise the life of the meter.

When to use Aquaread's pH meter

Aquaread's pH testing equipment is designed to be used in the field, and can either collect data instantaneously from a portable device or remain in-situ to collect long term data. pH is an important measure in water quality monitoring, for the reasons described above.

pH meters can be used in many applications, including commercial and industrial pH testing. Many industrial processes involve adding chemicals to water to achieve a specific, required pH. After its use, the water is then discharged as waste water directly into a water body, or perhaps through a local waste water treatment plant.

Industrial pH testing monitors the pH of the effluent water and, alongside other water quality monitoring parameters, ensures that this effluent water is safe to be discharged directly into a water body, without it having a negative effect on the local, and wider, ecosystem. An example of commercial testing may be using pH meters to measure the pH of water in a water treatment plant that produces drinking water.

pH meters can also be used for measuring pH in water bodies themselves, to measure any environmental changes.

Get into monitoring with Aquaread

If you would like any more information regarding our pH probes and testing equipment, or water quality monitoring in general please do get in touch. Click here to see our product range.