That much salt could soften the water a bit (at least here in Arizona, due to why it is our water is so hard). I doubt it would have much effect on the dyes. My mother always cleaned our work cloths (we were ranchers) with white vineager. Vineagar can aid in sterilizing, so I do use it in my final rinse, sometime with Florida Water, too, just to enjoy the sent it release when I press, or even stitch it. This way my studio smells like my late Father used to. It is more about sentiment than science, but I take my thrills where I can get them, yaknow?