Dissolved Oxygen Meter for Accurate Water Oxygen Testing

Dissolved oxygen is most commonly expressed in milligrams per litre (mg/L), which is equivalent to parts per million (ppm). It can also be expressed as a percentage of saturation (%) relative to the maximum amount of oxygen the water can hold at a given temperature and pressure.

When choosing a dissolved oxygen (DO) meter, consider the required measurement range, accuracy, sensor type, and practical features for your application. Most water quality testing needs a range of 0–20 mg/L with an accuracy of around ±0.1–0.3 mg/L. Electrochemical sensors are affordable and reliable, while optical sensors offer lower maintenance. A quality DO meter should include automatic temperature compensation (ATC) because oxygen levels vary with temperature, and support easy calibration, ideally with both one-point and two-point options for better accuracy. If long-term monitoring is needed, select a model with data logging or PC connectivity, and for fieldwork, ensure the device has at least an IP57 rating for water and dust resistance.

For most freshwater aquatic life, a DO level above 6 mg/L is considered healthy. Levels below 4 mg/L are considered hypoxic and stressful for fish. Levels below 2 mg/L are lethal to most species. In wastewater treatment, a DO of 2–4 mg/L is typically maintained in aerobic zones.

A dissolved oxygen meter measures oxygen dissolved in liquid (typically water), expressed in mg/L or % saturation. An oxygen analyser typically measures oxygen in gas phase (e.g. atmospheric or industrial gases), expressed as a percentage of volume. They use different sensor technologies and are not interchangeable.

For Clark-type electrochemical DO meters, the membrane cap assembly should typically be replaced every 2–4 weeks under regular use, or whenever the membrane appears damaged or readings become erratic. Always use the manufacturer-specified replacement membranes and electrolyte solution.

Yes. Most professional DO meters include salinity compensation, allowing accurate measurement in brackish water, seawater, and aquaculture systems with elevated salinity. Check the specification sheet of your DO meter to confirm salinity compensation is included.

These terms describe parts of the same instrument. The 'probe' (sometimes called an 'electrode') is the physical sensing element that sits in the water and detects oxygen — polarographic, galvanic or optical. The 'sensor' usually refers to the same probe assembly, especially in OEM or integration contexts. The 'meter' is the complete handheld or benchtop instrument that displays the reading. All the DO meters on this page include their probe/sensor; replacement probes (such as the MA840) are also available separately if yours needs replacing.