It does work. See the thread about posting pictures of clams, I just posted some of a year ago and today and the difference is noticeable.
Dip for 10 to 15 minutes. As much as you can match the conditions of the water from the tank to the FWD (temperature is and declorinated water please).
Also browse for responses to PM and FWD from Mbbuna, he may have additional information that I can't remember right now.
Omar