Many hobbyists and even some books recommend freshwater dips as a method of preventing the introduction of disease and parasites into the display tank. New fish are given a freshwater dip before being placed into the display tank to eliminate parasites. Unfortunately, this demonstrates a lack of understanding of most of the parasites that infect marine fish.
While freshwater dips are helpful for the treatment of some conditions, such as Amyloodinium and Turbellaria, they are ineffective for common problems such as marine "Ich" and Brooklynella. This means the unaffected parasites can still be introduced into the display tank.
Totally ineffective for the treatment of Cryptocaryon as the smaller theronts are protected from osmotic shock by the epithelial layer of the fish as they are actually under the skin of the fish. Only the parasites that have broken through the epithelial layer are lysed.
- (http://reefculture.com.au/blog/2009/09/cryptocaryon-irritans-marine-white-spot/): Porritt, M., Cryptocaryon irritans, Reef Culture Magazine, 1.