NH3 and NH4 together are often referred to as total ammonia nitrogen (TAN). Under normal conditions, NH3 (ammonia) and NH4 (ammonium) will both be present in aquarium water. The two exist at an equilibrium point that is governed largely by pH and temperature. However, salinity and the ionic strength of the water also influence this equilibrium ...
In true terms NH4 is a nontoxic substance in the aquarium, however due to the equilibrium which occurs between NH3 / NH4 at a given pH and temperature it is better to measure NH4 as an indicator of NH3 than nothing at all. Interpretation of NH4 to estimate NH3 is most often done by a chart supplied with the test kit or by a calculation online.
what is ammonium NH4 ? Water chemistry > What is ammonia NH3 & NH4? > what is ammonium NH4 ? If you have a worry or problem with NH4 then it is often a good idea to understand more about it. NH4 (ammonium) is a nontoxic salt, it is the ionised form of toxic ammonia NH3.
The movement in pH means that all of the ammonium (NH4) in the sample will be liberated to the NH3 form. The NH3 then reacts with the chemistry in the test to create the colour change that is measurable by the photometer or eye.
Nessler test kits measure ammonia NH3 and ammonium NH4. This is important to note and often missed as you will need to use a look up chart so see NH3 levels. New Salicylate based tests, with two sets of reagents measure NH3. If your ammonia test kit registers in shades of yellow to green to blue, its salicylate.