You need to get some sodium chloride test strips, they're a good bit more reliable than the conductivity test that your SWCG does. http://www.amazon.com/AquaChek-Salt-.../dp/B002OLP1L6 These are the ones I use (except I bought mine from leslies for a few bucks more).

This way you can eliminate the concern of other substances poisoning your salt conductivity test results.

Don't count on salt readings from your pool store either, as it's likely they're using a conductivity based test. This is the only test that my pool store consistently gives me bad results on (I have them run a test whenever I go buy something, then compare everything to my own results).