I put it in water for a few days and then scrub with a brush it takes all the dead stuff off easy this way. The water gets in and rehydrate the stuff and when scrubbing use boiling water to rinse off this helps to leach out phosphates from the rock. let sit in salt water for a week or 2 to get as much of the phosphates out as possible the water has to be on the worm side. In essence you are going to be cooking the rock and after a week or 2 reduce the temp to normal and get some live rock in there to seed the dead stuff.

Bill