To catch up a bit Salinity and Specific gravity are two ways to measure salt content of the water. Either one works.
Seeing no nitrate makes me think there isn't enough of a cycle to support your animal, and that is why you are seeing the ray show you stress but nothing is coming up in the water test. I'd also expect a trace ammount of ammonia by now as well. What all are you measuring when you check? (Sorry if you mentioned it already.) Ammonia, nitrite, nitrate, phosphate, pH?