Transfer sand bed?

[Duckhams]

It's best to start the new tank with new substrate. Even with meticulous regular cleaning you'll still get a big ammonia spike if you try to transfer the existing sand bed. I'd personally never reuse a sand bed, even after a thorough rinsing. I'd possible consider reusing a larger grain aragonite after a bleach soak to get rid of any remaining organic material that might cause an ammonia spike, and then a few days in fresh RO/DI but it's so much easier to start fresh and not have to worry about problems.