Storing the rock for a year is a long time to keep the tank running only for rock with what it sounds like algae growth.
1)I would take all the rocks outside using the garden hose and wash it well only with clean water, place it in an open tub let dry then cover and hide till next year
2)Sell the rock as I am sure you could get about $2-3$/lb
3)leave it be in the tank with a running power-head and lights off for roughly 3-4 weeks then remove let dry and store.