if you want to drop alk in salt mix its quite easy to do before even adding it to your system , again using the salinity values to monitor parameters like cal and alk is going to be impossible to do as every bucket of salt is different then the one before slightly and some drastically
you have to realize that salt alone almost always never keep alk and cal in check for mature tanks unless the tank is tiny and changes are large , in a heavily stocked hard coral tank with lots of coraline youll have to do about %50 per day to keep levels stable....thats not really a good way of doing it unless money is no object lol even then the jumps are not healthy either.
if you don't have corals im not sure why your worried about rtn on acros?
are you going ULNS?