shook...lolz
you must either be getting inaccurate nitrate results or there is algae growing in your tank and you cant notice it (maybe pleco has something to do with it) nitrates would not be 0 otherwise in a tank with a pleco w/o water changes for two weeks.
dont worry about it too much though, concentrate on the ammonia and nitrite. I'd say to be safe, wait till those two are 0 at the end of a week's time, and then do weekly water changes.