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Ammonia, in the aquarium hobby, refers to two chemical compounds, free ammonia (NH3) and ammonium (NH4+) together. Ammonia is a food source for nitrifying bacteria and is toxic to fish, amphibians and invertebrates. It is a key input to the The Nitrogen Cycle and an important parameter to measure when cycling a new tank.


What is it?

Free ammonia is a chemical compound of nitrogen and hydrogen with the formula NH3. Technically ammonia in water is called Ammonium hydroxide. In the aquarium hobby the term ammonia also refers to an ionized form called ammonium (NH4+). These are held in equilibrium in the water [Citation needed]. 'Total ammonia' (TA) or 'Total ammonia nitrogen' (TAN) refers to the total concentration of both NH3 and NH4+ in the aquarium water.

Where you have Ammonia, you will also have Ammonium. The ratio of one to the other varies on pH and water temperature. So it is important to know these two readings when measuring Ammonia in your tank to gauge how serious the Ammonia levels are. See the Links section for a Toxic Ammonia calculator. Here is a table showing the varying levels of ammonia against ammonium.

% Percent of ammonia from 'total ammonia'
Temp C/F pH 6.5 pH 7.0 pH 7.5 pH 7.7 pH 8.0 pH 8.5
20C (68F) 0.1250.3951.2391.953.8111.15
25C (77F) 0.1790.5651.7662.775.38015.242
28C (82F) 0.2210.6962.1703.3966.5518.156
30C (86F) 0.2530.7982.4823.787.45020.292

Sources of Ammonia

Primary sources:

Minor sources:

Testing for Ammonia

The concentration of ammonia in water is easily measured with widely available test kits. There are two common methods for measuring ammonia: Nessler measures total ammonia (NH3 and NH4+) [1] and Salicylate measures free ammonia (NH3) [2]. A test kit will use one or both methods. In the marine hobby if a test kit does not explicitly state it measures free ammonia then it is likely uses the Nessler method and measures total ammonia.

Some Water conditioners transform free ammonia (NH3) into ammonium (NH4+). As a result, Salicylate test kits will show a decrease in free ammonia while the Nessler test kits will not show any change in total ammonia.

The typical unit of measure is ppm (parts per million). In seawater ppm and mg/L are interchangeably since 1 ppm ammonia = 1.03 mg/L ammonia.


Removing Ammonia

A healthy aquarium should contain enough ammonia consumers to consume all ammonia produced naturally by the system. These consumers come in two forms:

When detectable levels of ammonia are found, these short term but immediate options are available:

Sourcing Ammonia

It is useful to add ammonia to a new tank in order to cycle it before adding any animals. There are products on the market which sell diluted ammonia as a cleaning agent. It is important to only buy a product with no additives (surfactants, perfumes, and colourants, etc.) that may pollute the water with other toxins. Usually the cheapest brands have the lowest additives.

Typical examples:


  1. Ammonia Test Kits: Nessler vs. Salicylate
  2. Ammonia Tests
  3. Mechanisms of Ammonia Excretion by Marine Fish
  5. US Environmental Protection Agency. Ambient Water Quality Criteria for Ammonia, (EPA 440/5-85-001) 2009. [1]
  6. Glodek, Garrett S. "Ammonia in the Closed System Aquarium," FAMA, June 1991.
  7. Barr Report (subscription required) - Fish Waste and Macrophytes paper page 9 - March 2007


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