Copperbands are notorious for being hard to get feeding. Live brine like puff said is a good idea. Also try frozen mysis. Hopefully you don't have any aggressive fish in there with them cuz that will make it harder also. Saltwater fish can go weeks without eating but if it's been at the fish store for a while it might have already been a while since it last ate so could be bad. If you have a well established tank with a lot of live rock and could be picking at the rock and getting some food. Good luck.