I'm not sure I completely understand the question, but if your are gonna change salt brands, I recommend:
1) You test the values of the new salt prior to adding it to your tank, make sure CA
are within acceptable ranges.
2) You match Salinity, temp and PH
of the new water with the tank
3) you switch over slowly, smaller water changes than you would normally do.
When I switched salt brands a couple months ago, I increased the frequeny and cut the % in half. ie: I was doing 5g every other week (on a 20G tank), when I switched I did 2.5g every week for a month, then went back to the normal routine.