0 nitrates on a tank that is not planted ? How do you keep it at 0 ? My tank is not planted and my nitrates stay around 20 ppm , that is with a weekly 40 to 50% partial water change . What kind of test kit are you using ? If you have been using API liguid test kit and not shaking the second bottle of the nitrate test long enough , you could have been getting a false reading all along . I used to follow the instructions and shake the bottle for 30 seconds and my readings for nitrates were always at zero , then I started shaking it for close to two minutes and started getting proper readings of 20 ppm .