Trouble reading Nitrate tester
I have the API nitrate tester. My problem is, if I hold the test tube vertically up against the card, it looks yellow (0ppm nitrate). If I hold it horizontally, it looks a little orange (5ppm). And if I take off the cap and look straight down, it's even more (10ppm).
What's the right way to read it?
20g tall - planted FW with celestial pearl danios (and some fry!), amano shrimp, and a cute neon blue Endler.