From Fish

Ammonia (NH3) is something that all aquarists will come into contact with at some point. It is one of the first chemicals you have to deal with when setting up a new aquarium.

In fact what hobbyists call Ammonia actually consists of two chemical versions - Ammonia (often called 'free ammonia' which is very toxic) and Ammonium which is far less so. These are held in equilibrium in the water. This causes a lot of confusion to beginners!

  • Ammonia - NH3, un-ionised. Often called 'free ammonia' to differentiate it from the ambiguous word 'ammonia'. It is a form of nitrogen.
  • Ammonium - NH4, ionised). This nitrogen version is far less toxic to fish and other aquatic animals. In fact it is so less toxic that we can ignore it and only regard its very toxic cousin.

The two types together in your aquarium water are called 'Total ammonia' (TA) or 'Total ammonia nitrogen' (TAN).

In the rest of this article, the word Ammonia refers to the un-ionised version NH3 - Free Ammonia.

  • Ammonium is a less toxic waste product of the metabolism in aquatic animals and is excreted via the urine by water animals.
  • Ammonia is produced constantly via the gills of fish, by the aquatic animals waste products decaying and the decay of plant and fish food.
  • Ammonia causes gill damage and eventually skin damage and death.
  • In general, ammonia is more toxic at higher alkaline pH values and as the temperature of the water increases.
  • Different species of fish and other aquatic animals have different tolerances to the level of ammonia in the water (in an ideal world this should be zero). Generally fry and young fish are more sensitive as well.

Test Kits

You can test for the level of ammonia in your tanks water. But test kits vary. Some test the 'total ammonia' (that is ammonia and ammonium) and some only test for free ammonia. It's wise to therefore check what your test kit is actually testing for.

Especially if you've used a ammonia neutralising chemical of some kind. These usually transform free ammonia (NH3) into ammonium (NH4+). So a test kit will show the presence of ammonia but its the far less toxic version. The two types are called 'Nessler' which does total ammonia and 'Salicylate' which shows ammonia (NH3).

  • Most aquarists are only interested in the more toxic version - free ammonia (NH3).

*Be very wary of water conditioners that just say they remove Chlorine and Chloramine. They often just convert chloramine into ammonia (they break the chemical into two parts, chlorine and ammonia, then just neutralise the Chlorine!). Buy a bottle that specifically says it removes ammonia as well as chloramine.

Key Points

  • Free ammonia is very toxic to aquatic life. It kills in aquariums at very low amounts. Any level above 0.02mg/l (ppm) is considered harmful.
  • The pH and temperature of the water will directly affect the amount of total ammonia that gets turned into the virtually harmless ammonium. See table below.
  • Ammonia in an aquarium can be rendered less toxic by adding a small quantity of salt to the water. See Salt article.
  • Ammonia is not toxic to plants in levels that would cause distress to fish, indeed of those plants tested, most preferred ammonia or ammonium as a food to nitrate [1].
  • Allowing any ammonia level in a tank to remain will cause an algae bloom.

Ammonia Toxicity

Ammonia varies in toxicity at different pH and temperature of the water.

Here is a table showing the varying levels of ammonia against relatively harmless 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) 0.125 0.395 1.239 1.95 3.81 11.15
25C (77F) 0.179 0.565 1.766 2.77 5.380 15.242
28C (82F) 0.221 0.696 2.170 3.396 6.55 18.156
30C (86F) 0.253 0.798 2.482 3.78 7.450 20.292
Generally, any free ammonia value worked out from the above
percentages over 0.02ppm is dangerous
  • To work out your own levels you'll need to know total ammonia level, pH and water temperature in centigrade. Then go to this web page - Free Ammonia-Nitrogen Calculator
  • In nitrogen sensitive fish like Trout, ammonia is about 6x more toxic than nitrite and about 13,300x more toxic than nitrate [2]

Removing Ammonia

There are many ways to remove or reduce levels of ammonia in an aquarium.

  1. Bacteria like Nitrospira will eat the ammonia and convert it to the less toxic nitrite chemical. This can take many weeks as they establish themselves in large enough quantities in a new tank.
  2. Perform a water change. This dilutes the total ammonia levels quickly and cheaply.
  3. Plants in a tank will soak up ammonia in order to grow. This works well but can take time.
  4. Buy special resins or rocks which soak up the ammonia. These are reusable and relatively cheap. Typical resin product names based on zeolite are Ammo-Chip or Ammo-Carb.
  5. Buy ammonia neutralising chemicals in a bottle. These can be expensive and can cause false readings in some test kits. But are virtually instantaneous in use and less work. Typical popular product is Prime by Seachem or AmQuel or AmQuel_Plus by Kordon.

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:

  • UK - Kleen_Off


  2. Barr Report - Fish Waste and Macrophytes paper page 9 - March 2007