Very good, reliable information
"Prevention:
Foods/Feeding, Livestock Loads. Nitrates are resultant from "too much proteinaceous food input, not enough output"... One easy approach to their limitation is to simply stock and feed your system lightly... particularly with foods of high protein content. Catabolism of protein (made up of amino acids, in turn the source of ammonia) from foods, wastes, decomposition is the root source of the precursors to nitrate: GIGO, garbage in, garbage out.
Some supplements and salt-mixes have nitrates of appreciable concentration in them. Read labels and if in doubt, test these by diluting into water, and using a test kit.
Detritus in the substrate can be a reservoir, manufacturer of nitrate. Vacuuming a portion of it along with your water changes can reduce this source. Similarly, mechanical filtration media that traps proteinaceous foods and wastes needs to be cleaned and/or replaced on a regular basis to limit these materials release, cycling in the system.
Wet-dry media in same-named filters are a huge source of nitrates. The aerobic bacteria cultured on their vast surface area readily produce nitrates. By and large, aquarists and their aquatic charges are best served by removing such media, converting the same space to live rock, macro-algae culture, either on an alternating light cycle with their main system, or leaving the lights on continuously."
Written by Bob Fenner