well either is prob just fine just keep it consitent i keep mine 1.021 - 1.023 99% of the time is 1.022-1.023 just don't have big swings in short amount of time
Specific gravity is just a tool to determint Salinity. Given the temp of the water and the S.G. you can determine Salinity. The Salinity should be around 35ppt for most reefs, 37 - 39ppt for Red Sea biotope tanks.
E.g. My salinity is about 35ppt at a s.g. of 1.025 and a temp of 83F.