Hi,
For anyone moving their tank:
Your tank is held together by silicone and plastic around the rims... Never ever move a tank with anything in it. The wet sand alone is super heavy. Just because others have done it, does not mean it was a smart move. It isn't worth it to take a risk, spring a leak and have to replace the tank.
Wen Tom... you don't need to keep any water, put your fish in tubs in the old water, with an air line, and heater if you need one. Set up the new tank with what you have in the old one. Use the sponges (as instructed earlier) to keep things balanced and don't clean anything off, such as the filters and pumps. Re-acclimate the fish to the new tank like you would a new fish you just purchased...all done! It will take about 2 hours...with new sand, 24 hours to allow it to settle and clear. Have your filters up and running to expedite that. With new sand you will have "new tank" issues. If you keep your old sand, and just add to it, you won't.
Keep the old tank, or use a tub...set it up someplace where you can cure rock in it... Then move the cured rock to the new tank once it's ready. The fish, and any coral, will be fine with what you already have transferred from the old tank.