using api test kit. I recorded it as between 5 and 20 ppm. Also, does it look like 10 and 20 look exactly the same shade on the card? if you use Api, does your 10 ppm and 20 ppm look like the same shade of orange? thanks!
The color actually looks like 5ppm to me but if you go into a well-lit room and hold the test tube against the white part of the card right next to the colors, you'll get your best reading. I go into my kitchen where I have good fluorescent daylight lighting and can tell things much better. Going outside also works. Incandescent lighting which puts out a yellow hued light makes it tougher for me to read the differences.
The good news is that it doesn't matter if it's 5ppm or 10ppm or even 20ppm. All three of those levels are low enough so they do not matter. There is a big enough difference between 40ppm which is the first level that really matters. When your nitrates get to 40ppm, it's definitely another indication that it's time for your regularly scheduled PWC (partial water change)... but remember, there are many other pollutants that we cannot test for so do not rely on the nitrate test kit as to when it's time to do a PWC. Do them on a constant and regular basis... I like weekly PWC's on my tanks and the percentage of water changed is determined by the bioload in the tank. In a lightly stocked tank, a 25% PWC once a week is probably sufficient. In a more heavily stocked tank, twice a week PWC's... or if the tap water and tank water baselines are close enough, then once a week larger PWC's (33% to 50%) are OK.
For all the men out there, men have a much higher rate of color blindness than women. Here's a couple of free sites to test your color blindness. The first two are kind of quick. The third one gets really deep and takes a little while to complete.
You won't see nitrites up hardly at all, the bacteria builds up very quickly that converts it. If your nitrates get high, do a water change. Obviously if the tank hasn't been set up long (or new fish are introduced) the longterm effectiveness of this method will be diminished.
I have the API test kit and the nitrate test is also the most labor intensive. Shaking the 2nd bottle solution vigorously for 30 seconds. then shaking the solution for one minute vigorously for 1 minute? lol I sure wish I had one of those vortex test tube shakers from when I worked in the lab.