It may or may not be ick. Like Tvan said, do your other fish have the same white spots? Sharks are very disease resistant, I've had ick outbreaks in my tanks before, and even when all of the bonny fish showed signs, my sharks never did. I'm not saying it cant happen, but its worth looking into before you medicate.
How fine is your sand? My bamboo sometimes stirs up my sand bad enough to get it all over him. Sometimes it will stay there for a few days. My sand is very fine though.