In October when I started this new tank I wentwith the large coarse sand (somesort of live carribean). I wanted a change from the very fine sand which was easy for the fish to displace. I was told when I bought it that there was no difference in either other than astetic reasons. Since than my sand that I do not move around when doing normal cleaning has somehow bound together and it almost impossible to move. It is almost a rock like formation, maybe attaching to the live rock. Has anyone ever experienced this before?