The Salifert kit can be read in low range by looking through the side of the vial instead of through the top looking down.
After mixing, hold the vial up against the white part of the color chart and look through the side. The color is amplified 10 fold so you divide the color chart values by 10. If you see 2 in the chart, it is 0.2. If you see 50, it will be 5 etc.
FWIW, if you are below 10 ppm nitrate, I wouldn't loose any sleep over it.
