Key Parameters - Ammonia

Fish excrete ammonia and lesser amounts of urea into the water as wastes. Two forms of ammonia occur in aquatic systems, ionized and un-ionized. The un-ionized form of ammonia (NH3) is extremely toxic while the ionized form (NH4+) is not. Both forms are grouped together as "total ammonia." Through biological processes, toxic ammonia can be degraded to harmless nitrates. Un-ionized ammonia levels rise as temperature and pH increase. Toxicity levels for un-ionized ammonia depend on the individual species; however, levels below 0.06 ppm are considered safe.

However, the intermediate form of ammonia, known as nitrite has been known to occur at toxic levels (brown-blood disease) in fish ponds.

The danger ammonia poses for fish depends on the water’s temperature and pH, along with the dissolved oxygen and carbon dioxide levels.

The higher the pH and the warmer the temperature, the more toxic the ammonia content can be. Also, ammonia is much more toxic to fish and aquatic life when water contains very little dissolved oxygen and carbon dioxide. Ammonia is toxic to fish and aquatic organisms, even in very low concentrations. When levels reach 0.06 mg/l, fish can suffer gill damage. When levels reach 0.2 mg/l, sensitive fish like trout and salmon begin to die. As levels near 2.0 mg/l, even ammonia-tolerant fish like carp begin to die. Ammonia levels greater than approximately 0.1 mg/l can indicate polluted waters.