It would be very rare for nitrates to go down to zero on their own at the end of a cycle without doing a massive waterchange. Unless you have a fuge full of cheato, a dsb or some other means of consuming the nitrate there is no way to get it out of a tank other than water changes. Yes I know that there will be some bacteria in the live rock that will support that process, but generally not enough to make your trates go all the way to zero.
If your amm. and nitrites are at zero, do a water change to get the nitrates down to below 20 and you should be ready to add fish. If you are going to be adding corals you want to get the trates down to as close as zero as possible. Below 20 is fine for fish IMO.