I have seen a HUGE fluctuation in test result ranges. Never used the Azoo brand, but I've had MANY people come in with tank problems who have "perfect" water, only to find out their parameters were way off with our tests. I've compared a couple of test kits with the Colorimeter (spectral color water analysis) that I have at the store. The kits that come closest were Salifert and on some, Fast Test (Instant Ocean). On the Instant Ocean Copper Tests, for example, they are so far off the Colorimeter results it's scarey. The Fast Test was showing the copper at .25, but the colorimeter showed .10 which would do very little to treat sick fish in our hospital tanks. Bring me a sample and your test kit and we can compare the results so you have an idea of the accuracy.