I have done fresh water dips before through advise of LFS, I have never loss a fish from doing this and it does help some, it is my understanding that the parasite literally explodes from the gravity change, I have watched events that took place while giving the fresh water bath and you can see them bursting, if you use lets say a dark bottom canister to do the bathing you will see the dead parasites on the bottom, but yes it does cuase much stress on a already stressed fish.