Nitrate (orange or red)
I am having trouble determining the color when I test nitrate. First of all 10 and 20 look like the same color and 5 is only slightly less orange, so I really can't distinguish in the 5-20 range. No biggie.
Question - when I put the test tube near the reading chart it is 5-20, but if I take off the top and look down the test tube it's red 40-80. Should I be looking down the tube when testing or not?