I'd say save yourself the trouble and wait on the water change. There's likely little that has occurred in regards to the nitrogen cycle that a water change would help. Just start adding 1/2 cup of salt to the back, let it mix up for a while, measure, repeat. As you get closer to your target reading ( I shoot for 35 ppm) slow down on the additions to be safe. The salt can be visibly dissolved but you won't get a true reading for a few hours. If you over shoot just remove some and top off with fresh water. You probably know this, but never add salt directly to you tank once it's stocked.
Also, you don't have to use a shrimp. If you happened to buy food already you can put a pinch in as well. You just need something to start breaking down.