Skiiming doesn't extract the salt from the water, but it does remove water so that when you top off (to replace the water to skimmer removed) you are replacing saltwater with freshwater. But unless you are skimming extremely wet & dump the skimmate daily, I wouldn't worry, your weekly water changes should fix that.
The skimmate does contain saltware. but it's not normally something you need to worry about. As not that much saltwater is generally being skimmed out. If you think you are removing a ton of skimmate, just check you salinity every few weeks.