Having zero nitrAte is highly unlikely in a system that has been properly cycled. NitrAte is the end product of the 'nitrogen cycle', so having no nitrAte means that the cycle is not progressing to completion. I suppose that you could get to zero nitrAte in a well-established, heavily planted, and lightly stocked tank, but I don't think that's what we're dealing with here.
My previous post was in reference to NitrIte... the intermediary in the 3-part cycle. Ammonia and NitrIte are quite toxic, while NitrAte is only toxic in higher concentrations.
A tank that is ready for fish will have...
0.0 ppm Ammonia
0.0 ppm NitrIte
<40 ppm NitrAte
Cheers,
-fpsiv