My husband and I are new to saltwater tanks. When we bought our current tank we bought it already set up from a guy that my husband works with. He had about an inch of crushed coral as his substrate. From my reading and from this forum I have come to understand that this is not a great substrate. My question is when I change it is it okay to just put sand over what is already in there or would it be better to move all the live rock, take out the old substrate and put in the new. Can I do this with the fish in the tank or should I remove them as well?