twilson,
Hi, I used to use korallia's on some of my previous tanks. What I did to keep the sand from blowing around, was place the powerhead about half way down the tank wall, and face it so it was blowing upwards. If the korallia is on the right hand side of the tank, have it facing up and to the left. The will allow for the water coming out of the powerhead to lower it's velocity before reaching the sand.
Also, as the tank cycles, I think you will notice that the sand blows around less.
Bare spots in the sand bed are not a problem. Issues have arisen when an established sand bed loaded with debris is disturbed by a powerhead that has fallen off the side of the aquarium. In your case, it won't be a problem. Although I could see sand being mildly irritating to the corals.
Good luck!