Regarding -
My wife and I both got slate gray fingernail moons from 5-20 ppm EIS when 
drinking quart levels every day. The solution was crystal clear, with very weak 
Tyndall.

Marshall

 
Did the fingernail discoloration ever go away?  How long did you drink such 
large amounts before it showed up? 
 
Just interested,  thanks -  B. Methven