I have done this twice - a 55 gallon and a 180 gallon. Both were switched over to sand in one weekend., with no spikes or lost animals. Many problems in tanks are undoubtedly due to the crushed coral. When you vacuum out your CC substrate, you are not getting at the junk accumulated underneath your reef structure. I had crushed coral for years and went through Nitrate and algae difficulties. Nitrates would go down after a water change and then go right back up. You will be so happy with a sand bed, I promise. You shouldn't need to "seed" your new sand if you have established live rock, as a great deal of the bacteria needed is contained in your rock, but I always do anyway. Start on a Friday night. Take out tank water before it gets all mucked up to fill whatever you will store your animals and live rock in until Sunday evening. Remove your animals and put them in your rubbermaid or whatever with powerhead and heater for a day or two till the sand settles, and then remove your live rock, which starts to yuck things up. Then start the gross part. Drain the water down as far as you can. Discard the water. When you see how gross it is you will not want to reuse it. Take out ALL crushed coral and all the smelly gunk and throw it away. Use this opportunity to clean your tank thoroughly before it is set back up. Use Vinegar if needed for tough cleaning jobs and rinse thoroughly. Good opportunity to clean everything else as well, powerheads, returns and so on. I would rinse the new sand three or four times to get rid of the fine dust. It will settle quicker that way. After the tank is cleaned you start to put it back together. Add the rinsed sand (some put egg crate under the sand bed to prevent any damage to the glass) to the tank. Then you have to add salt water. Some reefers maintain that you should use old water from the prior set up to speed up the process. There is very little in the water that is beneficial to the new set up. I would only do this if you can't afford all new water. I prefer to add a handful of "live sand" to the sand bed to seed it, as opposed to trying to use old water. You can get this from a LFS or a fellow reefer you trust. Adding the water is important. Go as slowly as you can, put something on the sand bed to pour or drip the water into to prevent as much disruption of the sand as possible like a shallow bowl, or a piece of plastic. It doesn't matter if it takes several hours to fill - this will affect how quickly you are able to see into the tank to put stuff back together. After the tank is full, add powerheads, filtration, heater to bring it up to temp and wait until you can see into the tank. This will take a day. If you have everything set back up by Saturday afternoon, you should be able to see into the tank to put the rock and critters back in by Sunday afternoon or evening. Put your live rock back in the tank, make sure your temp is good. If you want to acclimate anything delicate with fish and corals, that is fine too. Then put it back together. Should be a good weekend project. Keep us posted!