i picked this info up in two places.
kent's discription of their salt mix and red sea's fact sheet in their alk
pro test kit.
kent claims that their salt mix is designed for use with ro
water where as others are not.
red sea claims that low ca
readings are normal when using ro
water. that tap water has an avg ca
level of 100 ppm
and that you lose that when using ro
water. and low and behold my ca
level was apx 100 ppm
red sea recomends using crushed coral in the ro
storage tank. to make up the difference.
kent recomends using their osmo-prep product when not using kent's salt mix.
it does seem to reason that if you are a salt mix manufacturer you need to make a decision on whether or not to have proper chem bal when using averaged tap water or ro