Which article were you in?. Nitrates can be reduced quickly by large water changes, nitrate sponges, etc, however, once reduced the remaining nitrates in the substrait and rocks, etc. will tend to leach out for some time, so, expect the nitrates to rebound to some extend. in order to get them down and keep um down you have to determine what is driving them up. let me know which article you were in and Ill see if I can better explain the article.