[Beverly]

To quote from http://www.petsforum.com/personal/tr...marineich.html

Are freshwater dips effective?

Freshwater dips are generally ineffective in the treatment of marine "Ich" infestations. Trophonts burrow deeply into the epithelium where they are generally protected from external influences. Colorni (1985) found that even after 18 hours in freshwater, infected fish still have trophonts attached in the same positions as they had held before the freshwater treatment. The trophonts later detached and completed their life cycle as normal.

Trophonts penetrate the epithelium which causes a loss in osmoregulatory capability. Infected fish are less able to cope with a sudden and drastic change in the ionic concentration of their environment. This is likely to cause further stress to the fish which will impair their ability to acquire immunity to the parasite.