Ammonia (NH3) is excreted by fish directly into the water, and is also released from the breakdown of solid waste and uneaten food. Ammonia is highly toxic to fish, but is usually removed from the water by the bacteria which live inside the filter.
The only way to know what the ammonia level is, is by testing the water with an Ammonia test kit. A regular testing will prevent damage caused by ammonia poisoning.
Colombo Ammonia Aquarium Test Kit contains 40 tests.