How deep is your substrate? I actually have 3 inches of substrate and I removed a couple of leaves from the bottms and planted very deep. The cories can tend to rustle up the substrate sometimes but the problem your having is not all that different from everyone else who starts a planted tank. They will eventually root and not float up. Also remeber that if they are just planted then they might take a while to get acclimated to your tank. Take heart and know that they will root and then you'll have so much you won't know what to do with it.