Nitrate is an organic substance broken down from ammonia. Waste from fish is first in the form of ammonia (a deadly compound to marine life) and comes from solid waste and urea. Ammonia is then broken down by bacteria into the form of nitrite, which is a less toxic organic substance. Then nitrite is converted into  nitrate, which is not at all as toxic as ammonia, but can be in if left to accumulate in large quantities. You are probably wondering how to remove nitrates from your aquarium. This can be done by mostly effectively from periodical water changes and also by a process called denitrification. This process is when nitrates are biologically consumed by some plants and other small organisms in the aquarium and released into the atmosphere as a gaseous state (nitrogen). Some people like to place large quantities of plants or caulerpa into their refugiums or tank displays because these forms of algae use considerable amounts of nitrate in order to grow. When the algae grows excessively consuming nitrate from the aquarium, the aquarist can then harvest the plants and algae therefore removing nitrates from the aquarium. In some cases, aquarists place marine plants into the sump (beneath the cabinet section) of their tank to take out the nitrate and this method is quite successful. Advanced technology has led some aquarists to the use of a denitrification "tower" unit placed in a sump designed for specific bacteria which consume nitrate and convert it into free nitrogen gas. This method is also effective however the best results will occur from periodic water changes. Changing roughly 20-25% of the total water volume every 2 or 3 weeks will show dramatic results and probably lead to less algae problems.

    There are several common methods of nitrate removal suggested. I would strongly recommend periodical water changes and the use of marine plants in a brightly lit sump because it is the most natural process. Nuisance algae is a clear indication that too much detritus has built up throughout the tank. Detritus is purely organic material and causes nitrate levels to sore in the aquarium. Siphoning detritus off rocks and out of the substrate is also a great way to effectively remove nitrate concentrations. If your tank looks like a mess, that is your glass is completely covered in algae, your substrate filled with detritus, and your livestock in poor conditions, then follow these procedures: