I have a 72 gallon bow front tank. I have had it set up for about 8 weeks. It has cycled. I have a wet/dry filter and protein skimmer. I have about 65 lbs of live rock so far and 3 clowns and 2 convict gobies. I intend for it to be a reef tank. I started out with crushed coral on the bottom. Then someone told me that I needed about 3 inches of sand. He is from a reputable aquarium store in my area, he said that it would be perfectly fine to add it on top of the crushed coral. Now another pet store says, absolutely not! Take out the crushed coral or it will die and start stinking and eventually crash my tank. I have since asked several people and get the same two answers back and forth. Can anyone give me some good advice on the matter? PLEASE?!