That's too bad, but it can be cured.
Ich is a parasite and must be killed in order to rid your tank of infection. While water changes are important during the infestation, PWC alone will not cure your fish.
Heat and salt are the most natural ways to kill the nasty little things, which are only vulnerable in what is the free floating stage of their life cycle.
http://www.aquariumadvice.com/forums/f17/if-you-think-your-fish-have-ich-38796.html
Slowly heat the tank to 86 degrees. Any lower, and you will only increase its reproductive cycle. It is recommended to raise the temperature by one degree every 12 hours.
Use only nonidodized salt to further treat the tank. The salt will help kill the parasite and help ease the infection in the fish and help ward off secondary infections common with the infestation.
There are many different recommendations on the amount of salt to use. I've had the best resutls (total cure, no deaths) using one tablespoon per 10 gallons of water.
Keep up the salt and heat treatment for at least four days AFTER the last white spots disappear from the fish.
If you wish to use a commercial medication instead, try Kordon. Avoid ich cures that contain formadahyde, malachite and copper. They are more toxic to your fish and not only can kill off inverts, can make the tank forever toxic to snails and shrimp.