What is Ammonium / Ammonia

Ammonium (NH4+) is a positively charged ion (or cation) that is formed by the addition of a hydrogen proton to ammonia (NH3). Ammonia is found naturally in water, but if it is found at higher than natural levels this is a sign of contamination. This is why it’s so important to test for ammonia in water.

Aquaread Ammonium /Ammonia Water Sensor

The Ammonium water sensor is an Ion Selective Electrode (ISE). It measures charged ammonium ions found in the water. By using a complex calculation the sensor is also able to measure the ammonia concentration in the water.


Key Features

  • Solid state ISE sensor.
  • Ammonium Measurement range 0 – 9,000mg/l.
  • Ammonium Resolution: two auto range scales: 0.00 – 99.9mg/l, 100.0 – 9,000mg/l.
  • Ammonium Accuracy: +/- 10% of reading.
  • Ammonia Measurement range 0 – 9,000mg/l.
  • Ammonia Resolution: two auto range scales: 0.00 – 99.9mg/l, 100.0 – 9,000mg/l.
  • Ammonia Accuracy: +/- 10% of reading.
  • Simple to install on a wide range of Aquaprobes.
  • Sensor life of around 6 months depending on usage.
  • Long storage shelf life.

Ammonia vs Ammonium

Both compounds contain nitrogen and hydrogen. Ammonia contains three hydrogen and one nitrogen while ammonium contains four hydrogen and one nitrogen. As a result, ammonia smells pungent and ammonium has no smell.

Why test for Ammonia in water?

Ammonia levels higher than around 0.1 mg/L usually indicate polluted waters. Ammonia is used in fertiliser and animal feed production as well as in the manufacture of plastics, paper, rubber, etc. Ammonium ions are a waste product of animals and, in the case of fish, are directly excreted into the water.

Our ammonium sensors can be fitted on many of our probes, below are some examples.

To see all of the probes that feature ammonium sensors please visit the Products section



Advanced portable multi-parameter Aquaprobe.



The Aquasonde-2000 has 2 spare ports. They can house either 1x ISE sensor and 1x Optical sensor. Or it can house 2x ISE sensor.



Advanced portable multi-parameter Aquaprobe.

Solid State Sensor

This is a solid state sensor in that it is not gel-filled. The advantage of this kind of sensor over those offered by other manufacturers is that the sensor will not deteriorate over time so long as it's dry. Gel-filled sensors have a finite life from the point of manufacture.

A new, dry solid state sensor can be stored for years without degradation, making this a superb ammonia measuring instrument.

Calibration and Temperature

Successful calibration of an ISE is fairly complex. On its initial use, a three-point calibration is required. Generally, this is at 10ppm and 100ppm of the sensor’s specific calibration solution, with the third point intended to characterise the effect of temperature on that specific sensor. The third point is a second calibration at 10ppm however, this calibration point must be at least 10 degrees colder than the initial point. This is because the measured concentration varies with temperature as well as the actual concentration of the ion.

The good news is that once this calibration is complete, subsequent calibrations do not require the third point to be re-done making future calibrations much simpler to perform.


An ideal ISE sensor would only allow the ion in question to be passed through the membrane. However, in practise all ion selective electrodes suffer from interference from ions which are similar in nature to the target ion. For this reason, ISE Electrodes are not recommended for use in brackish or salt water due to the high level of interfering ions.

Simple installation

Installing the ammonium sensor into an Aquaprobe is a very simple process. Simply unscrew the blanking plug from an appropriate aux socket, apply some silicon grease to the thread of the sensor (grease provided) and screw in the sensor. After installation full calibration is required.