Method Got my SN - purity test questionable

[yo_no_soy_el_pollo2]

I'm using the purity test recommended by the PPH. It has a max of 25 ppm on the nitrite side. The nitrate side has a max of 500 ppm. I did the test with 2 1L water bottles, marking their levels with a marker first. One annoying thing is that one bottle had slightly more water in it than the other one, although I'm not sure exactly how much. I put 1g SN in one bottle, shook well. Poured out some of the other 1L bottle to make some room. Then I used a syringe to pull out 25ml of the first bottle into the second, and filled up the rest of the room with tap water to the fill line.

The control stick changed color only the tiniest bit, probably not enough to really register on the color scale included with the tests. The second stick seemed to be right on 25 ppm nitrite, which seemed great, but it also registered about 250 ppm on the nitrate side. I'm confused by that. Shouldn't there be very little nitrate? After I was measuring out 26g vacuum sealed bags (with dessicant) and cleaning up, I looked at the test stick again and the colors faded a fair amount. At that point it matched the color of about 5ppm nitrite.

Should I be concerned about that? Maybe I should get a second brand of test and re-run it. I also probably should have done it with 100% tap water instead of bottled water + some tap water, for consistency.

I did order another batch of SN from a different source. Assuming I actually get it I'll do the test with it as well.

 

[yo_no_soy_el_pollo2]

I got my second batch of SN, the test results seemed the same as the other brand. I also bought another brand of test kit. I tried testing at different concentrations with both kits. They seemed inconsistent at different concentrations, but both brands of SN seemed to be consistent at those concentrations. I'm going to assume they are both good enough. The PPH does say that you shouldn't actually need to test it, since it's likely too cheap to be faked. I measured out 26g packets (to account for measurement being off a bit) and added desiccant, vacuumed sealed, then wrapped in foil (I don't think it's light sensitive, but the original containers were opaque). Saved for a rainy day.