You've been given lots of great advice. If you don't run through an effluent chamber it is not likely that you will be able to raise the pH. Fresh air might help a bit, but probably not much according to your outdoor testing. I also agree though that pH 7.9 isn't a big deal. I don't think your salt has anything to do with it either. Try an effluent chamber.
Could you expand on "my ALK drops out"? What number does it go from and to? How long does it take to change?