when i had my 20g reef i moved 3 times, and never had any spike.
I broke down the tank live stock first,
LR i placed in large tupperware containers with aquarium water about half way full.
bottled about 25% about 5 gallons
and left the sand bed with about 1" of water on it.
moved tank, stand
then replaced in reverse order.
it took about 6 hours for the whole process
its a pain in the back also.
but by keeping the LR submerged i had 0 die off
and there for had 0 amm. 0nitrate 0 nitrite spike
so i would say in total i kept about 1/2 the water
oh yes trow your filter media in the water to keep its bacteria alive.
do this and you should have no problems,
good luck!