What is the proper ammonia level in saltwater tanks?

In both fresh and saltwater tanks, ammonia needs to be absolutely zero at all times. This extremely toxic compound is produced constantly by fish and will build up very quickly unless steps are taken to remove it. There are bacteria that will remove ammonia and turn it into non-toxic compounds - this process is called the nitrogen cycle. In freshwater tanks these bacteria live mainly in the filter. In saltwater tanks, they are more likely to be found in live rock or live sand, which are the most natural ways to keep a saltwater tank clean.