Sally -- Feeding the live sand bed is easy. The idea is to break up the food small enough that the fish can't steal it all on the way down, so it settles to the bottom for the benefit of the sand critters.
I use a plastic syringe with a long piece of rigid airline tubing attached like a needle, secured to the syringe with a short section of telescoping rubber airline tube. It should be long enough to reach the bottom back of your tank.
Then just thaw the Prime Reef or whatever in a small sample cup filled with a few milliliters of tank water. Suck the food up forcefully into your long syringe and spit it out back into the cup a few times until it breaks up into small pieces. Now just squirt it out onto the sand under/behind the reef. When I do this, everything from hermits to Nassarius snails comes running. Even the bristle worms and 'pods will sneak out in daylight to eat.
Just be careful not to overdo it so much you set the tank to cycling again, producing ammonia or nitrites. Start with just a little corner of a cube of Prime Reef and work up slowly feeding every other day or every third day until you see what your sand can handle.
To gauge how much uneaten sand food is left over, about 12 hours after feeding the sand you can use a small spare powerhead to gently blow any uneaten food out from under/behind the rocks. If too much is left over, cut down a bit next time. This is great for your filter feeders, too!
Good luck.
[ July 20, 2001: Message edited by: BReefCase ]