I soaked my old live rock in bleach and water, then rinsed it several times really well. Then I put it outside for a week. With the rain and the sun, the rock further bleached and finally dried out. It came out really well. It is really amazing though how long it took for the
corraline algae to die off. That stuff is really tough.
So now I'll soak it in a large Rubbermaid barrell filled with RODI water and a powerhead and change the water every few days for a few weeks. Then I'll place it back in the sump.