Ammonia build-up results from a break-down of fish metabolism. As ammonia (NH3) constantly converts to ammonium (NH4+) and vice versa, ammonia test kits usually measure both, resulting in a total ammonia 
(ammonia-N) concentration.
In an established tank, the reading of this test must show an undetectable level at all times. A detectable presence of total ammonia requires immediate action.
Ammonia is highly toxic in freshwater tanks, but even more toxic in reef and saltwater environments. This is due to a higher pH level that causes the presence of ammonia gas, which in turn is far more toxic and easily water soluble.
Even low concentrations of ammonia-N severely stress fish, making them vulnerable to diseases therefore shorting their life span. Accumulating ammonia will not only be highly toxic and cause severe stress for the fish, it will be lethal!
Ammonia toxicity is significantly influenced by temperature and pH. The lower the temperature and pH the more ammonia can be tolerated.
Lethal ammonia concentrations at a pH of 6.5 are 0.73 ppm, while at pH 8.5 only 0.17 ppm are considered lethal to inhabitants.
A fish tank kept at 68 degrees F can tolerate more then twice the amount of ammonia as a tank kept at 86 degrees F.
