Funkness

In those size tanks I would take the reverse path. Carefully siphon all the water out and save it. Carefully remove the rock and livestock. Then just remove all the crushed coral. Replace with dry never been used or pre-seeded live sand, refill with the water you removed, and you should be good to go. Treat it just like a tank move.

Whats the best type of dry sand to use

I like the caribsea special grade reef sand. Just rinse it a lot. A ton of dist in the dry version.