If you don't have fish, do a 100% water change. Start fresh. It will make your life a lot easier.
No point of leaving any in. Just keep the filter media moist while the filter is turned off. Even if you left 10% of the water in the tank and had 150 nitrate, you'd be left over with 15 nitrate which is too high. You should aI'm to keep nitrate around 5 ppm, never exceeding 10 ppm. 20 ppm is the absolute highest your fish should ever see if you go on an extended vacation or something.