Amoníaco

What is it?

Free ammonia is a chemical compound of nitrogen and hydrogen with the formula NH3. Technically ammonia in water is called Ammonium hydroxide. In the aquarium hobby the term ammonia also refers to an ionized form called ammonium (NH4+). These are held in equilibrium in the water [Citation needed]. 'Total ammonia' (TA) or 'Total ammonia nitrogen' (TAN) refers to the totalconcentration of both NH3 and NH4+ in the aquarium water.
Where you have Ammonia, you will also have Ammonium. The ratio of one to the other varies on pH and water temperature. So it is important to know these two readings when measuring Ammonia in your tank to gauge how serious the Ammonia levels are. See the Links section for a Toxic Ammonia calculator. Here is a table showing the varying levels ofammonia against 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
Sources of Ammonia

Primary sources:
Fish excrete ammonia as a waste byproduct ofmetabolism. In particular, fish excrete free ammonia from their gills and ammonium in their urine. It is suspected invertebrates excrete ammonia in some form as well. The amount of ammonia excreted will vary with amount of food eaten.
Decaying organic material from dead animals and uneaten food. As the material decomposes, nitrogen is released which is converted into ammonia by bacteria.
Minor sources:tap water
salt mixes
Testing for Ammonia

The concentration of ammonia in water is easily measured with widely available test kits. There are two common methods for measuring ammonia: Nessler measures total ammonia (NH3 and NH4+) [1] and Salicylate measures free ammonia (NH3) [2]. A test kit will use one or both methods. In the marine hobby if a test kit does not explicitly state it measuresfree ammonia then it is likely uses the Nessler method and measures total ammonia.
Some Water conditioners transform free ammonia (NH3) into ammonium (NH4+). As a result, Salicylate test kits will show a decrease in free ammonia while the Nessler test kits will not show any change in total ammonia.
The typical unit of measure is ppm (parts per million). In seawater ppm and mg/L areinterchangeably since 1 ppm ammonia = 1.03 mg/L ammonia.
Toxicity

Free ammonia is highly toxic to aquatic life. It kills in aquariums at very low amounts. Any level above 0.02 mg/l (ppm) is considered harmful.
Ammonium may be toxic to marine fish, especially if the pH differs significantly from natural seawater (e.g. during shipping) [3]
Free ammonia causes gill damage, internal organ damage andeventually skin damage and death. Typical symptoms include:
ragged or frayed fins
cloudy eyes
rapid gilling
lack of appetite
more susceptible to disease
In general, ammonia is more toxic at higher alkaline pH values and as the temperature of the water increases.
Ammonia is not toxic to plants in levels that would cause distress to fish, indeed of those plants tested, most preferred ammonia orammonium as a food to nitrate [4].
Rough guide to toxic levels of free ammonia:
0.020 to 0.049 (ppm) is considered 'tolerated' but will cause long term harm to its growth, immune system, health, etc. especially to eggs or very young animals.
0.050 to 0.199 (ppm) is perhaps tolerated for only a few days and is very harmful.
0.200 to 0.499 (ppm) is perhaps tolerated for a day or two and will probablykill.
0.500+ (ppm) is deadly and will probably kill within a day.
Individual species of fish, amphibians, invertebrates etc. vary enormously on their tolerances of low levels of ammonia and the issue is made further complicated as young are far more susceptible to ammonia than older animals.[5] [6]
In nitrogen sensitive fish like Trout, ammonia is about 6x more toxic than nitrite and about...