In my opinion, You are stressing yourself out about the new salt mix too much. Coral and rock will survive and thrive in a wide range of parameters.
The easiest thing to do is take the salt mix that you intend to use and mix up a gallon and test it.Use a salt mix specifically for reef tanks that is Ca enriched. To make life easier, if it is in the ball park, go with it. I have done many tank transfers and found the freshly mixed salt to adequate for the job at hand.
Get the transfer done and then worry about your ca and alk after. Unless you have a tank full of ca devouring corals that will knock your levels down in a day,they will survive a day or two with a slightly lower Ca level.
The easiest thing to do is take the salt mix that you intend to use and mix up a gallon and test it.Use a salt mix specifically for reef tanks that is Ca enriched. To make life easier, if it is in the ball park, go with it. I have done many tank transfers and found the freshly mixed salt to adequate for the job at hand.
Get the transfer done and then worry about your ca and alk after. Unless you have a tank full of ca devouring corals that will knock your levels down in a day,they will survive a day or two with a slightly lower Ca level.

