|Danger:||> 0.3 ppm|
Ammonia is a product of the breakdown of proteins. The waste excreted by most animals is either ammonia or something that will break down to ammonia (urea, undiggested protein, etc.).
Ammonia is the starting point of the nitrification process. Certain bacteria use it as an energy source and nitrite is produced as they extract the energy. There will always be ammonia present in an aquarium, but once the biological filtration is established, ammonia is processed so quickly that it is undetectable by hobbyist test kits and does not present a problem. Until the biological filtration is established, ammonia may be present in high concentration which is why you need to wait before adding livestock.
Ammonia is present in water in two forms, un-ionised ammonia (NH3) and ammonium ion (NH4+). Ammonium is a charged ion and as such is not generally taken up by organisms as so can be regarded as non-toxic. Un-ionised ammonia, however, is very toxic. Normally only a very small percentage of total ammonia is present as un-ionised ammonia, but there can still be enough present to be lethal to organisms in the tank.
The percentage of un-ionised ammonia present in water is dependent on the pH, temperature and salinity of the water. The higher the pH or temperature, the higher the percentage. Figure 1 shows the relationship between un-ionised ammonia and pH for a number of different temperatures at normal salinity (35ppt). While it is not important to understand the exact numbers, knowing the trends below can help you deal with ammonia problems.
 Figure 5. Changes in speciation of phosphate, silicate and ammonia with pH. The red box shows the range that pH is predicted to change within.
The toxicity of un-ionised ammonia varies from organism to organism but anything more than around 0.1 mg/L of un-ionised ammonia present as nitrogen can cause issues for life in the aquarium. This equates to anywhere from 0.3 and 1.0 mg/L of total ammonia (as measured by most test kits) depending on the pH and temperature.
Action When Detect Ammonia
An established tank should never have detectable ammonia, however, if there is major die off of organisms, such as form the addition of a large amount of liverock, you may get readings of ammonia. If there are organisms in the tank they need to be protected from the toxicity of the ammonia, and there are a number of things that can be done.
Water changes are a good way to dilute ammonia but remember a 25% water change will only reduce the ammonia by 25%. A number of large (50%) water changes may be required in order to save the lives of organisms in the tank.
Manipulation of the pH and temperature is generally not a good idea, however, if the pH is already low (7.8-8.0) it would be wise to leave it there as this will reduce the percentage of un-ionised ammonia present.
There are a number of ammonia detoxifying products on the market which can be used if water changes are not possible. These include:
- Prime and AmGuard (Seachem)
- Ammonia Detox (Kent Marine)