API Nitrate Test Kit Question.

[Gage Zamrzla]

So I have a fairly heavily stocked 75g tank and when testing recently my nitrates were reading in the 80ppm area, I have a very large root system of pathos hanging in the tank and do a 40-60% W/C each week and my nitrates are generally around 20-40ppm steady. I decided to test my water again with an identical, API nitrate liquid test kit that a friend gave me not too long ago, I saw an eye popping difference when the results showed up at approx 10-15ppm, I tested again using my friend's kit, shaking the bottle as instructed once more to make sure it was really mixed up, the result after shaking the bottle for a solid 30 seconds straight showed up at 20ppm. Now I know I have enough common sense to see something was odd here. I tested a fourth time, leaving the previous three tests on the table for comparison and the original test again comes up with an 80ppm result. So this is what I'm looking at

Test 1: My API Nitrate test kit, 80ppm
Test 2: Friend's API Nitrate test kit, 10-15ppm
Test 3: Friend's API Nitrate test kit, (shaking the bottle for another 30 seconds) 20ppm
Test 4: My API Nitrate test kit, 80ppm

I also tested my tap water and the result shows >5ppm Nitrate. All tests were done the same, measurements, time shaking bottles, and all given at least 10 minutes to give a final result.

I checked into expiration dates based on the code given on each API test bottle and they all check out.

I'm know I'm opening myself to a joke by saying I'm not an idiot on a public forum but I'm very much confused at the moment. Any input on this situation? I am aware that it's almost 3a.m. but this is making no sense to me at the moment. I'll also be purchasing a brand new Nitrate test kit in the next few days for a certain answer and in the meantime I'll be doing a water change tomorrow for good measure but I'm open to any suggestions, input, corrections.

 

[Gage Zamrzla]

I should also mention this isn't any kind of panic mode situation, the fish are showing no signs of stress, eating normally, and you can see clear through the tank lengthwise so this doesn't seem to be an emergency but I'd certainly like to properly assess the situation before it potentially becomes one.

 

[redfan]

The api Nitrate bottle #2 needs to be shaken like **** for at least 2 mins prior to testing .. then you still follow the 30sec shake (as in the instructions) before adding to the water. Did you do this? (shake for 2 -3 mins before even starting any testing)

I have had odd test results in the past which have stabilised since I started following the above.

 

[Gage Zamrzla]

I didn't shake it that long, I've heard the reason shaking is necessary is that there are basically two chemicals, one thicker than the other that needs to be properly mixed. If that's the case would you assume that not mixing properly would give a low reading? What changes did you see once you started following the above procedure?