Becky sounds like you aren,t running any phosphate remover oe\r vacuming the bed. Algae loves phosphates so that is the first order. You must be running somekind of box filter if your'e running carbon, you need to get a small prepackadged bag of phosgard made by seachem and run in your box filter. Change it out when it gets tan in color. This is probably as important as the skimmer, phosphate is algae food. The next order of bussiness is the sand bed. Sorry to tell you but you have to be able to vac that shallow of a bed when you do your water changes, so the substrate has to be course enough to not be sucked out when you vac. I would set the live rock on the bottom and put you bed out front of the rock. There are no snails or critters that well get rid of detritus, it has to be vac't out in a 1" deep bed, along with your skimmer and the phosgard. This well take sometime to get straightend out but it well happen with time. Remember we have to get this algae food source out of your tank.