There is limited truth to this although it is not a cure
. The parasite can actually survive in FW
for quite a long time. The effectiveness of FW
dips is limited to the outer layer of the skins surface only and the parasite merely becomes dislodged. Any trophonts that have worked their way deeper into the epithelium will be unaffected.
It is a commonly used treatment but is also one of the least affected. You end up placing the fish back into an infested tank where tomonts have undoubtedly encysted making new little pests. Without an affective treatment in place that interupts the lifecycle of the parasite you are not accomplishing anything and the net result is usually a severely stressed fish but still infested.