Catherine,
  A TDS meter is not the same as a PWT, though. I thought the PWT is best for 
testing DW and for estimating ppm (from uS) of the finished CS? 
  paula
  ----- Original Message ----- 
  From: C Creel 
    Try TDS

  http://www.automatedaquariums.com/h_tds1.htm

  Regards,
  Catherine