Ammonia And Nitrite

Ammonia and nitrite are key players in The Nitrogen Cycle, as discussed in our section on Aquarium Cycling.  And both ammonia and nitrite are deadly to fish and invertebrates, even at extremely low levels.


Ammonia in aquariums is the by-product of waste produced by our aquarium inhabitants.  Overfeeding, decaying food, fish urine and feces, and dead and decaying fish and coral all contribute to aquarium ammonia levels, otherwise known as Total Dissolved Ammonia.

Total Dissolved Ammonia can occur as highly toxic ammonia (NH3) or as less toxic ammonium (NH4+), depending on the pH of the aquarium water.   At lower pH levels, total dissolved ammonia occurs as ammonium.  Ammonium changes to poisonous ammonia as pH increases.

Aquarium ammonia levels of even 0.01 ppm (parts per million) is considered harmful to marine life.  Fish will appear uncomfortable — they will be breathing heavily, hiding or darting about the tank in panic.  At 0.01 ppm of ammonia, corals and invertebrates will simply perish.

ammonia and nitrite

Clams consume small amounts of ammonia


Bacteria in the aquarium’s biological filter convert ammonia to nitrite (NO2).  While nitrite is less harmful than ammonia at the same concentrations, it is still deadly .  Concentrations of 0.1 ppm of nitrite will wipe out corals and invertebrates, while concentrations of 0.3 ppm will result in death for all but the hardiest of fish.

Testing For Ammonia And Nitrite After Your Aquarium Has Fully Cycled

Every new saltwater aquarist purchases test kits to monitor ammonia and nitrite levels during the aquarium cycling phase.  Not only is testing important at this point but it also provides a glimpse into the wonder of Nature at work as we chart out the rise and fall of ammonia and nitrite to zero levels.

But as enthusiastically as we test for ammonia and nitrite while the aquarium is cycling, we all but ignore ammonia and nitrite after our tank has fully cycled.  Most of us turn our attention to testing for nitrate (NO3) only.

But it is just as important to perform monthly tests for ammonia and nitrite for about 12 months after a saltwater aquarium has fully cycled.

This allows us to keep an eye on how our biological filter is doing, and enables us to address any problems that may arise.  And don’t forget to monitor the behaviour your new aquarium inhabitants as well, looking out for tell-tale signs of ammonia and nitrite-induced stress.

When in doubt, test!

Seachem’s Ammonia Alert

Seachem’s Ammonia Alert is a particularly important piece of equipment for any aquarium that is less than a year old.  This little plastic card has a color wheel indicator on it that changes color when ammonia is present.  It can detect ammonia in aquariums from 0.02 ppm.  Depending on the amount of ammonia present, the color wheel will indicate Safe, Alert, Alarm and Toxic levels.  It detects ammonia levels as low as 0.02 ppm. Ammonia Alert lasts for up to one year in the aquarium and can be used in both salt and freshwater.

In our section on New Tank Syndrome, we will discuss the effects of ammonia and nitrite poisoning in new aquariums as well as how to prevent it.

Read more about other Aquarium Water Parameters:


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