Something else to think about is, even though your cup isn't "filling up", their is still a good amount of junk on the neck of the skimmer. I would still clean that out, all your bubbly skimmer water is touching it which can get into your tank water. None the less, you'd be surprised how much is actually there caked on the neck. I think your skimmer is set just fine by the pictures, but empty out the cup and clean out the whole top piece. If it keeps getting like that, just keep cleaning it. It is still skimming something.
And I agree with everyone else, look for a new source of water. I don't know about now, but on black Friday I got a bunch of salt on Amazon. They had the 5 gallon buckets, or the 58 lb boxes of instant ocean for 38 bucks. And check your local forums for an RODI unit. I picked one up for under $100 bucks from a reefer, and am glad I did. The conveince and peace of mind of good water quality is more than worth it.
Good luck, best of luck!