red sea iron test

In response to Dirk: I have the red sea iron test kit.  It's very easy to
use, but somewhat difficult to read between 0 an .1 ppm as for 0 ppm the
color is a pale blue, and for .1 ppm, its a pale blue with a light tinge of
green.  The two colors are quite close.  The rest of the scale isn't bad,
but the low end is a bit difficult to read with precision.  
"Candle?  What candle?  I don't see any candle, it's too damn dark in here!"