How do you test for Nitrates?

[Midway]

Hi there,

Well, I'm bit confused here as how to properly test for Nitrates for saltwater. I have a testing kits (API) I bought a couple of months ago from JL. I think I was testing the wrong way. I was adding 10 drops of bottle # 1, shake a bit, added 10 drops of bottle # 2, shake a bit, waited for 5 minutes, no nitrates detected 0 ppm. (happy as a camper).

For some reason one of those days, I was bored or something, I read the instructions that came with the kit, well I did it as the instructions said, WHAT??!!??? turned out my nitrates were very F#@@#!@$#$% HIGH more than 40 ppm. I thought, what the heck is this?? cause the instructions say, add 10 drops of bottle # 1 shake a bit, now this is where the change is, shake bottle # 2 for at least 1/2 minute (and they say these steps are critical for the accuracy of the test) then shake the heck out of the tube for at least a minute. WOW high nitrates when I see the tube against the color chart. Now I wanted a second opinion, I took some water to Pisces so they can test my nitrates, maybe my kit was old or something. The guy there (very young teenager) did the test, did not even shook the bottles and of course no nitrates detected. I told him that when I was doing as the instructions said, I was reading very high nitrates, but this kid told me that shaking the bottles and the tube does not do anything to the test (I don't think so).
I even bought another testing kit from them to compare tests with the kit I already have, same results.

Any other parameters like amonia, nitrites, phosphates, etc. come out normal. the only one that I'm fighting with is Nitrates.

I have a lot of cyano in one of my tanks and I think high nitrates are contributors to that.

So should I follow the testing instructions?

Thanks for your inputs.

Manny