Garnet,
 
Some time ago, like maybe a couple of years, there was quite a lengthy  
discussion of what PPM of CS is needed to cure something. As I remember, the  
conclusion was that ppm is largely irrelevant -- 2or3 ppm being as effective as 
 20 
or 30. There is a technical name for this condition, but I don't remember  
it.  Perhaps some of the technical people know what it is so that you could  
find the discussion in the archives.
 
GeorgeA