1 cup of skimmate does not equal 1 cup of fresh saltwater...
But yes... skimming does remove some salt..
You must always measure salinity... adjust as needed..
But dumping in 1 cup of fresh saltwater each time you remove the skimmer cup is not the way to go..
Somewhere someone did a fairly extensive test on skimmate and did record salinity levels,etc.. of whats in the cup..