Less than 5ppm NO3.
Plants get squirrlely under 2-5ppm and generally stunt.
N stunts growth more than other nutrients.
P is very hard to stunt a plant with on the other hand.........
It may slow growth, reduce O2 production etc.
Honestly, while you can do and maintain low NO3, it is something you need to be really good about otherwise you will louse the tank up, most folks do.
If you decide this is something you must do against this advice, well, try less light, slow things down, so that it is much easier to maintain and dose 2-5ppm ranges of NO3.