How to test for ammonia in water.

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Testing for ammonia.

When organic matter from plant and animal residues breaks down, the first product formed is ammonium. If water is well oxygenated the ammonium is quickly converted to nitrates. Ammonium can also be secreted by fish or can come from fertilizers or industrial wastes. If water becomes overloaded with organic matter there may not be sufficient oxygen to convert all the ammonium to nitrate. When this happens ammonium levels can build up. High levels of ammonium can be toxic to organisms especially fish. Where there is ammonium present, some ammonia is formed in a type of balance. The normal balance is biased towards the less harmful ammonium. Ammonia is called the unionized form and is more harmful to fish than ammonium. Therefore tests for ammonium are used to detect overloaded or low oxygen environments.

In acidic (less than pH 7) solutions less harmful ammonium dominates but as pH rises harmful ammonia levels increase.

At 20 deg C here is the proportion (%) that harmful ammonia makes up of the total ammonia and ammonium: pH 7, 0.4%; pH 7.5, 0.99%; pH 8, 3.83%. Source Lamotte Smart Colorimeter Manual. So take a pH reading when measuring ammonia-N then multiply by the percentage given (interpolate if necessary) to get harmful ammonia.

The proportion of harmful ammonia also increases with temperature. For example between 10 deg C and 20 deg C the proportion of harmful ammonia approximately doubles at the same pH.In acidic (less than pH 7) solutions less harmful ammonium dominates but as pH rises harmful ammonia levels increase.

Chemical tests sometimes give the total ammonia and ammonium as the ammonia nitrogen (NH3-N) value. The conversion factor to get to just ammonia / ammonium is approximately x 1.2. Sometimes the test will give a value as ammonium.

 

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