Does it look like tfish have been sprinkled with salt? If they do, they have whitespot, also known as ich.
The first thing to do is increase the temperature slowly to 30 deg C (85 F). While it is warming, go and buy a whitespot medication, there are several on the market. You must add the med exactly as it says, don't stop when the spots disappear. Whitespot is caused by a parasite that has three stages in its lifecycle. The first is where it is attached to the fish, it has a coating over it which we see as the spots but the coating protects the parasite against the med. Then the parasite falls off the fish and falls to the bottom of the tank as a kind of cyst. Again, the med can't get at it. Finally, the cyst splits open and free swimming parasites go looking for a fish to infect - this is the only stage where the parasite can be killed so there must be some med in the water when every last cyst splits open. Increasing the temperature speeds up the cycle so you get to the end faster.
If you have scaleless fish in the tank (eg loaches) you may need to reduce the dose. Read the instructions. And if you have any snails or shimps the med will probably kill them, so take them out of the tank first. If necessary just keep them in a lidded box and change the water daily. Make sure you run fresh carbon in the tank for a few days after treatment has finished, escpecially if you have shimps and snails as the med must be completely removed before they can go back in.