Yes, I have done this with a few of my fish and it has worked out great. Get a container, preferably a clear one so you can watch the fish from the side view, of DECLORINIZED fresh water. NO SALT. Make sure it is the exact temp of your tank. Also check the
pH. Make sure it is at least around 8 or so. Pull the fish out of your tank and put him in the container and watch him. He really wont like it too much but after a min or 2 you will see flakes coming off of him. These are parasites that can not handle fresh water. They will fall off the fish. After about 5 minutes skim the fish out and put him back in your tank. Do not put that water back in your tank!! You will see little STUFF settle to the bottom of the container. It might take him a few minuets to recover but he should be fine. If he freaks out really bad , get him out and back in your tank. If you try it let me know what happened. GOOD LUCK