Here is the thread I was talking about
:
http://www.reefcentral.com/forums/sh...hreadid=537999
And what Calfo said:
"yes.. if you use demineralized water, you have taken the bad and the good (mineral hardness) out of it.
Salt mfg's formulate sea salt presuming and average mineral hardness to your water. They have to ride the fence on this one because some folks using their salt have soft or Ro/DI water... while others are on the opposite end of the spectrum (extremely hard water).
Thus... if you are on the soft end... you need to remineralize your fresh water before salting it... else you are handicapping the buffering ability (ALK) of your new saltwater before its even used!
Common seabuffer is all, mate. If you want to get fancy... some companies (Kent is one as I recall) make products for remineralzing RO/DI water "