so i tested my water today to see if it was clean of nitrates and it was ZEROOO, now i know these things are super accurate and my tank could have like .2, .5, or what ever and the test wouldn't read it, but i got a idea. what if u did like half or 3/4ths the amount of water in the test tube that your suppose to and then just did the test, that way it would be more concentrated to read better to see if it truly is zero.
No you need to use a test kit that reads in a low range, such as Salifert or Lamotte. Unless your using bio-pellets or vodka along with bacteria (aka pro-biotics). Then you don't have zero nitrates, probably low but not zero. What kit are you using, I have seen api throw false negatives and the Ocean kit always shows zero.
I think it is very possible your nitrates are very close to 0. Your tank is established, 3 years old? w/ a pretty well maintained deep sand bed. Your sps, for the most part, keep color, and you keep up on your water changes.
If you really want to get a real acurate reading, you have 2 options-
Get a low range test kit or have someone that does test your water.