I'm not sure why the sand has anything to do with how your tank is set up. If you are considering an under gravel filter because of the holes in the bottom of the tank then yes you should use crushed coral, but I would strongly recommend patching the holes and drilling the tank for an overflow box, under gravel filters tend to lead to higher nitrates in marine systems. In either case I would use dry sand, not live which is more expensive since you are paying for water, is difficult to clean and has little if no benefit.