Nitrate Tests - are they all garbage? Round II

[mwp]

So I can't find my original post. We kinda agreed that maybe Nitrate tests aren't all that accurate, but this latest round of "tests" has me more than miffed. What's the DEAL? Here's the scoop:

Last night I utilized 4 different Nitrate Tests to check the nitrate levels in 4 aquariums. All were done within an hour or so; I think these results are pretty "reliable" in so much as each test was tried with 4 different samples, and 4 tests were used. Instructions were followed to the letter (including times of agitation / wait times before reading results)

The tests in question are Seachem, Instant Ocean (brand new test kit), Aquarium Pharm Liquid Test, and Jungle's Quick Dip Strips. Here's the results (all PPM):

Tank #1
SC - 5
IO - 10
AP - 40
QD - 40

Tank #2
SC - 50 or higher
IO - 10
AP - 80
QD - 40

Tank #3
SC - 5
IO - 10
AP - 40
QD - 40

Tank #4
SC - 10
IO - 10
AP - 80
QD - 40

NOT one of these tests acurately matches the results given by another brand of test consistently. Worse still is that the two NEW tests (Instant Ocean 1 part powder and Jungle Quick Dips) gave the same result for every tank tested. It's interesting that these are both "one part" tests. The "two part" tests (Seachem and Aquarium Pharm) gave pretty consistent reading, in both cases showing the differences from tank to tank, yet they don't match up with each other EITHER.

It seems that the one part tests simply don't work even remotely well, as both showed the same results across the board for 4 distinct samples. I don't have any long term data on these two new tests yet.

In looking at long-term data from the two part tests, both seem to accurately track each other's results (i.e. if Seachem shows a rise, AQ Pharm will as well). The problem is that the "distance" between the results is consistently "huge" (i.e. 5 ppm on Seachem vs. 40 ppm for AQ Pharm) and to make matters worse still, at TIMES, these results will almost merge (i.e. getting a 30 ppm on Seachem and still a 40 ppm on AQ Pharm)...the distance between the levels "detected" by these two tests isn't proportional or consistent.

Is there ANY test out there that's a) accurate and b) consistent? I hate having shelled out probably $75+ for 4 nitrate tests only to find myself not really trusting ANY of them!

FWIW,

Matt