Yeah the salinity is fine. Just get the fw to the same temp as the qt. Put in an air stone for 15-30 min to oxygenate the water. Then put the fish in for 5min max. Add a little bit of the qt water to the fw and that will help balance out the ph.
You are looking to see if anything falls off the fish. Flukes will look like opaque sesame seeds and will fall off the fish within the first 3-4 minutes.
Here is a link to a great video of it:
https://youtu.be/Po_dvEr5DL0
