Say your salinity is 1.023, I think you could just take off the 1 because that is the SG of one mL water. So you could say .023 times 100 (gal) / whatever #gallons are left and add the one back. So, .023 times 100 / 80 plus 1. (salinity 1.0287) Right?
I guess measuring conductivity is more...
