Moving a LARGE tank

[MitchM]

Both times that I did it, I had an extra (second) large tank and a few weeks overlap between move-in/move-out dates.

That allowed me time for set up of the new tank at the new place, transfer of the corals, fish and as much existing water as possible.

Next was tear down and transfer of the old tank to the new house. It's guaranteed that plumbing set-up and solvent curing times are going to take longer than you plan for.
You don't want to rush new salt water cycling either.
My set up is a 204g main tank with a 180g sump.

How did you get the 300g downstairs in the first place?

Mitch