A properly cycled aquarium won't have a nitrate reading of 0ppm, especially with that many fish.
Did you shake bottle number 2 of the nitrate test for 2-3 minutes? There are particulate matter in bottle number that clumps up if the bottle is not shaken every week. The directions for the nitrate test are as follows
1. Fill vial to the line with tank water.
2. Put 10 drops of bottle number 1 into filled vial.
3. Shake briefly
4. Shake bottle number 2 for 30 seconds (or 2-3 minutes if you have not used this bottle in more than 1 week).
5. Put 10 drops of bottle number 2 into vial.
6. Shake vial for 1 minute.
7. Let it sit for 5 minutes.
7. Compare vial with the color chart on the card. Make sure the white part of the card is behind the vial, and not touching it when making the comparison.