I've noticed over the past months that my royal gramma seems like its building, it goes into one area and is either breaking up the rock or moving the sand around it, its actually where two rocks come together. I thought maybe it was clearing out where it sleeps, but it tends to sleep on the other side of the tank behind a couple different rocks. Today I saw the oddest thing, it reminded me of a sparrow gathering twigs for a nest. It swam across the tank with a piece of macro-algae in its mouth, then tucked it in the same area mentioned above. Unfortunately I couldn't grab my video camera quick enough. Gotta love fish watching!