...work out the required dose and dose nsw before doing the water change. I have no idea if that's right, but it's my current plan. :) Or just #yolo and see how things look by dosing as normal the tank and doing water changes weekly without adjustment..
My personal experience: Ive been testing...
...test everything. Put in new rocks, leaving room for old rocks. Confirm salinity/temp/etc.
But the next step few options i'm considering
1.) #yolo and move the rock + fish into the new tank. Hope that in combination of increase in water volume + skimmer along with no increase in bioload that...