Al... I recommend getting an E.C> meter...a nice and easy one is the Blue-Lab Truncheon that is sold in hydroponic stores for testing nutrient solutions...
I quit checking ANYthing other than E.C. on my system...my tapwater has an E.C. of 0.8 I was testing Ammonia like crazy and ignoring other tests until finally one day I came across my old truncheon and dipped it in there after I had lost 2 rays... The E.C. at that point was 2.2-2.4..YIKES... so it doesn't even MATTER what it was, the water had too much stuff in it...
Now I have been monitoring the E.C. on a regular basis...I have been keeping it around 1.2-1.4 including just a tad bit of salt with each water change.
I do not know what the E.C. would be with a full salt dose...I havn't done that in a while...but it would be easy to stop the dripper, add the appropriate amount of salt and measure the E.C. once it has a chance to fully mix in a couple hours...after that...just keep adding back salt as the E.C. drops with your drip...
It also is a perfect way to regulate your drip... it may take more or you could get by with less...just compare system E.C. to sourcewater E.C.
Mike