This is branching off my original thread about my insanely high nitrate readings from both tap and tank. It occurred to me to question whether the test is accurate? I'm almost at the end of my bottles for nitrate, and I'm wondering if the concentration of chemicals is higher at the end of the bottle (from maybe not shaking it up properly when it was fuller)? I'm aware it's easily possible to get false negatives if you don't shake them up properly, so can it work the other way round? The reason I'm questioning it, is that to begin with I didn't shake them up as much as I should have (a cursitory tumble before testing) and I got several 0 readings which at the time I thought was excellent since my tank is heavily planted. I used to get low readings (lightly orange) and then I learned that you needed to shake it up really thoroughly. So I started and that's when I started getting really high readings (very much in the red). I know that they are crystals in the second bottle, could they have settled and now that its almost empty and I am shaking the life out of it, whether that is the cause of the high readings. Sorry, I'm rambling, but hopefully you get what I'm asking. Thanks!