They have ick most likely, go to the pet store and get some ick med. to put in your tank. Do the white spots kind of sparkle? If so that's ick. If they look more like dull white spots, then you need to get antibiotics for your tank. I pill for every 10 gals. and take your filter out, the carbon effects the antibiotics.

To avoid Ick, make sure that when you do a water change, that the water you add into the tank is the same temp as the water that was in the tank. Ick is caused by changes in water temp, hot to cold, cold to hot, etc. in most cases.

Or else if you added a new fish to the tank that might of had ick and he spread it to the others.

Also do a water test, make sure everything is right in your tank, if not that can be part of your problem and the fish are ill.