Reefeer was explaining a brackish water bath, which is good, but totally different than a FW dip.
I don't like FW dips, because you are compounding the problem. A fish with ich is taken out of its home, dropped in FW, stressed beyond belief, and then put back where it got the ich in the first place. As we all know, stress is one of the biggest causes of ich outbreaks, but people still do FW dips??