Ammonium / Ammonia

Ammonium NH₄ and ammonia NH₃ are in an equilibrium that depends strongly on the pH value and also on temperature and salinity. The higher the pH value, the more the balance is on the toxic ammonia side.

Ammonium/ammonia is released into the water through animal excretions. There it is either immediately absorbed by corals and algae (ammonia assimilation) or oxidised by specialised bacteria via nitrite to nitrate (nitrification). It is uncertain whether a possible anammox reaction takes place in the aquarium, in which ammonia and nitrite are reduced directly to atmospheric nitrogen.

Drop tests, test strips and photometer tests measure the sum of ammonium and ammonia. If the pH value is not known, these tests are of no value - unless nothing has been detected. For an assessment of the toxic ammonia content, at least the pH value must be known. The pH value should be measured at the end of the lighting period. In a table or with the help of an ammonia calculator, the toxicity can be estimated. Ammonium/ammonia cannot be determined with ICP.

Ammonia is toxic from approx. 6 µg/l (0.006 mg/l).

Ammonia calculator: https://www.aquacare.de/index.php/en/aquaristic/aquaristic-info/waterparameter/ammonium-calculator.html