If all of a sudden your fish looks like it has been sprinkled with table salt the chances are your aquarium fish is suffering from the Ich fish disease. This is a very common parasitic disease that any aquarium owner has dealt with. This parasite multiples quickly and can spread to other fish and continually re-infect the original fish. Once you see those white spots normally the infected fish will continually scratch themselves on anything they can in the tank from gravel to the decorations. The white spots will ulcerate, releasing more of the microscopic, free-swimming, infective tomites to attack other fish in the tank. A fish infected with Ich can also be very susceptible to a fungal infection.
The Ich fish disease is not necessarily fatal but can completely wipe out a whole tank of fish quickly if not treated immediately. I have personally dealt with Ich a few times with all but once all the infected fish making a full recovery. The one time when I wasn’t successful treating the Ich fish disease I lost about half my fish in the aquarium. Quickly treating Ich is the key to success with this parasitic fish disease.
There are many treatments designed specifically to address the parasite causing Ich. Even if you remove the fish infected with Ich from the tank you still need to treat the water so the other fish in the tank do not become infected by the remaining parasites. This is where having a hospital tank cycled and always ready to go is invaluable. Just having a 10 gallon tank off to the side where you can put a sick fish in a moments notice will save you tons of money in the long run. Ich is not fatal if treated but it is highly contagious and can spread quickly if action is not taken quickly.