Ammonia poisoning  (New tank syndrome)

All animals produce nitrogen compounds as a by-product of normal daily metabolism. Most species of fish produce ammonia which is very toxic in the aquarium.

Under normal circumstances, fish in the wild donít have ammonia toxicity problems since they live in millions or even billions of gallons of water and their ammonia becomes quickly diluted and incorporated into the nitrogen cycle where it is detoxified by naturally occurring bacteria.

Ammonia poisoning is one of the most common water quality problems in newly established recirculating systems, shipping containers, or following medication of fish by bath treatments with certain chemicals (e.g., formalin).

Ammonia is the primary nitrogenous (protein breakdown) waste product excreted by fish and is also produced when organic matter, including uneaten food decomposes in water.

Ammonia can cause acute mortality but most often it present as a sublethal stress.

High levels of ammonia in the aquarium are probably the number one killer of pet fish. Any measurable amount of ammonia indicates either an overloaded aquarium (too many fish or too much food) or an inadequate filter.

The ammonia level in a fish farm is usually lowest at the water inflow and highest at the outflow.

When fish are introduced into a new tank in which the biological filter is not well established. The ammonia rapidly rises killing the fish (new tank syndrome).

The biological filter contains nitrifying bacteria as nitrosomonas species that convert ammonia to nitrite.

Professionals commonly ask at what point should ammonia levels be considered dangerous? The best answer is that any detectable ammonia in an established aquarium indicates a filtering deficiency. Ammonia should not be detectable in a pond with a healthy biological filter at all times.

The ideal and normal measurement of ammonia is zero.


Causes of high ammonia level in the water:

1.  Inadequate number of nitrosomonas bacteria lead to accumulation of ammonia in the aquarium water.  If the biological filtration capacity is too low to remove all the ammonia produced by fish the ammonia level will rise. The total amount of ammonia that can be converted to nitrite depends on the amount of biological filtration in the tank where the aquarium water passes over a surface that has nitrosomonas bacteria thus the biological filtration is greatest when there is a high water flow over a large surface area.

2.  Antibiotics that are dumped into the water can damage a biological filter resulting in elevated ammonia levels.

3.  If the biological filter cleaned vigorously removing most of its bacteria sudden rise of ammonia will occur.

4.  Uneaten food, decaying substances and ammonia generated by excretion of fishes are the largest sources of ammonia in a fish farm.

5.   Algae and nitrosomonas bacteria are the major consumers of ammonia so ammonia tends to increase during fall and winter because of decrease in algal and bacterial metabolism at low temperatures.

6.   Massive death of algae (occurs either spontaneously or caused by algicidal chemicals) not only reduces ammonia assimilation but also increases the level of ammonia by the decaying dead algae.

7. Too many fish (Overcrowding) in an aquarium with an un-established or inadequate biological filter.


Clinical signs of ammonia poisoning:

1. Acute toxicity is associated with anorexia (stop feeding), lethargy, swim erratically, behavioral abnormalities and neurological signs.

2. The pond water is frequently cloudy and in some cases dead fish and uneaten food may be present (contributing to the problem).

3.  Some fish produce excessive mucus in response to the elevated ammonia and may appear cloudy or pale. The eyes may be opaque and the gills pale or swollen (diffuse gill epithelium proliferation).

4.  Increase blood and tissue ammonia levels causing elevation of blood PH and osmoregulatory disturbance.

5.  Decrease disease resistance resulting from stress.


Diagnosis of ammonia poisoning:

1.   History: over crowding, new fishes may have been added without increasing filtration, change in the management of the system (a new person is feeding the fish, the type and amount of food has changed, the frequency of water changes has decreased, dead plants and fish are not removed immediately), recent addition of chemical, newly established aquaria and recently washed biological filter or failure of the biological filter.

2.  Clinical signs.

3.  Measurment of the level of unionized ammonia: test your water and confirm whether or not you have an ammonia problem in your aquarium or pond by commercially available kits.  Ammonia is present in two forms:

a.   Unionized ammonia (NH3) which is toxic to fish.

b.   Ionized ammonia (NH4+) (ammonium) which is less toxic.

 The amount of unionized ammonia NH3 in water depends on the PH, temperature and salinity of the water. High PH and temperature and low salinity favor the presence of unionized (harmful) ammonia.  If the unionized ammonia is greater than 0.05 mg/L it should be reduced as quickly as possible.



1.  Frequent change of water or increase the water flow will reduce the ammonia level.

2.  Adding fresh water will dilute the ammonia concentration.

3.  Transfer the fish if the ammonia level reaches 2.5 ppm.

4.  Avoid accumulation of excess feed or even stop feeding the fish if detected in an established pond.

5.  Decrease the PH of the water (every 1 unit decrease in PH there is a ten fold decrease in unionized ammonia). But this must be done with great care because rapid drop in PH cause other problems.

6.  Increase the biological filtration capacity.

7.  Reduce the stocking density in the tank.

8.  Many medications are toxic to nitrifying bacteria so after use of such medications the biological filter must be re-established.

9.  In ponds prevention of ammonia toxicity is better than therapy since ammonia cannot be rapidly removed from the pond (by not overstocking, overfeeding, or overmedicating, the chances of an ammonia problem are greatly reduced. Coupling these strategies with an adequately functioning biological filter will insure that ammonia toxicity will be something you only read about).