You mean 'curing' rock I assume? Curing is just allowing the dead or dying material (usually from shipping) on the rock to dissolve off in a separate container rather than in your tank, thus crashing it with excess ammonia/nitrates. Curing rock may not get rid of harmful critters if they are hardy.
Cooking the rock means to literally boil it in hot water to kill-off troublesome algae that just won't go away. It turns live rock back into base rock, and you have to start from scratch to introduce beneficial bacteria back into it.
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George
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