low nitrates?

Ever since switching over to EI dosing and cranking my CO2 up I havent been doing much testing (after things stabalized). But recently I went to measure nitrates and it read zero. I have also had some BGA constantly at the tips of some of my tallest plants and also around the waterline on the glass. I found it hard to beleive with EI and my somewhat overstocked tank that my nitrates were 0, so I grabbed one of my mardel quick dip strips and it was saying 20-40ppm. Well, my api test kit was a few years old so I ordered a new one. Just got it today, and after doing 50% wc and adding my 3/4 tsp KNO3 (75g) I was still getting zip. The color never shifted from bright yellow. So I grabbed the dip strips and again, it was reading ~20ppm or so.

So whats the deal, should I be worried about low nitrate? Are the API nitrate tests not accurate? ANyone else have the same problem.

I bet thats it. I havent read an instruction from thise kits in a couple years. Though I usually give the bottle a quick shake, no where near 30 seconds worth. I will retry, and if I dont get something expected, I'll try the bucket method.

BTW, I meant to say unexpected at the end of my last post. Gotta love not being able to modify ones post later.

Hmm, I again got zip for nitrates in the tank, so I tried testing in a container. I put in about 1 gallon water and 1/8 tsp KNO3 and the best I could tell was 10ppm. I havent had the chance to look up how much 1/8tsp per gallon is in ppm, but according to Ice's thinking even that seems low, but atleast it was clearly changing colors. [Edit: I see Rex posted the ratios while I was typing, and that my testkit was reading in that ballpark]. Now I guess I should be adding more nitrate to my tank, being that I am already dosing EI this seems like alot, and I am somewhat overstocked on the fish - its funny when I was thinking to check nitrate I was expecting to see a high enough number that I'd probably quit dosing KNO3 and leave that to the fish. Go figure.