Quarantine your fish. When acquiring new fish or treating your current sick fish, use a small (10 or 20gal) aquarium as a quarantine tank. Allow new fish and plants to live in quarantine for about two weeks before introducing them to your show tank. This way you can make sure they are healthy and will not introduce disease to your already established fish. This can also make it easier and cheaper to treat the fish. You will not be medicating fish that don’t need it, and if your quarantine tank is smaller than your show tank, you will use less medication. This is more effective, and your fish’s survival rate will go up.
Note: Normally sick tropical fish should be removed from an established aquarium and placed into a hospital or quarantine tank. With fish Ick the whole tank needs to be treated together, so placing the fish into a quarantine tank is not recommended.
One of the alleged benefits of this treatment is the resulting conservation of energy for the affected fish. Reef fish have to constantly drink saltwater and excrete the salt to maintain the proper osmotic balance. Lowering the salinity of the surrounding environment eases this energy demand on the sick fish, thereby allowing them to expend more energy towards fighting the infection (Kollman, 1998 and Bartelme, 2001). On the contrary, keeping fish in low salinity means that they don't "flush" their kidneys sufficiently. After long-term exposure, this can cause kidney failure and kill the fish (Shimek, pers. comm..)
Variations of this method (and the likely source for the original idea for the treatment) have been suggested and used successfully by Colorni (Colorni, 1987 and Colorni & Burgess, 1997). They involve moving the infected fish between two tanks with the tanks being cleaned and dried in between uses or removing a sand substrate and replacing with new sand every three days. I don't like the idea of handling a sick fish that much using the tank transfer method. While fishnets are designed to be soft and supple, it can still be dragged across the fish's eye. I have found the more you have to manipulate a fish, the more likely it is to contract a secondary bacterial infection like pop-eye or cloudy eyes. The substrate removal method is interesting. The sand is supposed to be an ideal media for attracting the encysting parasites. Removing the sand every three days removes the tomonts with it. Utilizing aragonite sand for this purpose is expensive (unless you happen to live somewhere that Southdown sand is readily available) and very messy. Silica sand is widely available, cheap, and will create slightly less cloudy water, but it is still not as clean and easy as the water change method. I have found the water change protocol to be just as effective and considerably more practical than either of Colorni's methods.