adding live sand to a running system

Will it be o.k. to remove the substrate from a running system and replace it with live sand? and will this have to cycle, or will the live rock take care of the nitrification cycle>

 

You can do it but not all at the same time. Do about a 1/4 of the tank at a time. Removing it all at once will cause problems since you'd be removing considerable bacteria.

 

Why use Live sand just use a good aragonite and let what you have seed it with the needed bacteria just replace it the same way as described before half then wait to do the other half. L/sand offers no magic bullets to help with anything except to separate you from your money. If you feel you want Bio Diversity just get some fauna infested rubble from a someone on line. Or just a pound or so from a LFS.