Perhaps nothing? Lots of folks transfer tanks all the time. If all your rock is going into the new tank, you shouldn't have a problem. You can either clean your sand before putting in, or use new sand, doesn't matter. The rock is the bulk of your biological filtration. So as long as that goes, and your water params are the same as your old tank, you should be good. You can read more about the sand/rock NEW TANK RULES here.