NT Labs Marine Lab Ammonia Test
Most ammonia generated in an aquarium is the result of the digestion of proteins by fish and other aquarium animals. Ammonia can also be released by the bacterial breakdown of excess food and other organic matter.
It is extremely toxic to fish and invertebrates, especially in a marine aquarium due to the higher pH found in saltwater. Ammonia is broken down into nitrite by the beneficial bacteria in your aquarium filter or live rock and then subsequently into relatively harmless nitrate.