Ammonia (NH3/NH4+)

Ammonia is the first product of organic decomposition in the aquarium. In non-ionised form (NH3) it is toxic even at very low concentrations.

Detailed explanation

Ammonia occurs in two forms in water: NH3 (free ammonia, toxic) and NH4+ (ammonium, much less toxic). The proportion between the two depends on the pH and the temperature: the higher the pH, the more the toxic NH3 portion increases. For this reason, in marine aquariums where the pH is high even traces of total ammonia become dangerous.

In a cycled aquarium, nitrifying bacteria convert ammonia into nitrites and then into nitrates. The problem arises when the production of ammonia exceeds the capacity of the bacteria: too many fish, excessive feeding, a dead fish not removed, a filter washed with tap water.

In ponds the risk of ammonia is greater in spring. The temperatures rise, the koi start eating again, but the biological filter is still half asleep from the winter cold. This phase shift causes the ammonia peaks typical of spring awakening.

The same principle applies to brackish water as to marine water: high pH amplifies toxicity.

Reference values by aquarium type

How it is measured

Drop test (Salifert, API, Sera). Caution: Most tests measure total ammonia (NH3 + NH4+). To know how much toxic NH3 there is, you need to consider pH and temperature. Coralia Lab does this calculation automatically.

What happens when it is too low

No problem. Zero ammonia is the goal.

What happens when it is too high

Fish breathe on the surface. The gills become red and produce mucus. The corals close completely. Above 0.5 ppm by NH3 in marine aquariums there is a risk of mortality within a few hours. In ponds, koi become lethargic and stop eating.

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