White spots = ICK or a lot of stress. Not sure how stress could have got to the clown unless you did some drastic changes. Temps, pH, ??? no idea. could be any of that.
Have you tried to quarentine the clown yet and see what happens? If you think it has ick or an infection go get garlic and add a few drops with the food you feed the tank, this will help build up the immunity from what i was told and read. i use it and my clowns are looking great. no more white specs on them.