You can turn off the pumps and scoop out whatever is in reach. Then siphon out the rest. Your rockwork will likely shift, so you may want to move your corals to a holding container with tank water. If you go that route, you can seriously breakdown the tank.
1) Corals in a frag tank vessel
2) Rock in a clean vessel keeping it submerged in tank water
3) Scoop out / siphon out all sand. Clean the tank.
4) Reset the rockwork and corals with tank water from #1 plus new saltwater. (The rock in #2 can be shaken in that saltwater to get rid of detritus before moving it into the tank again).
As long as the rock stays submerged 99% of the time, you won't have any cycle. Have plenty of new saltwater ready for this project.