Cooking live rock and live sand was a very popular method of preventing potential nuisance life forms from entering into one’s aquarium. The idea was to put the rock into large containers of saltwater, devoid them of light for long periods of time, and perform routine water changes. Unfortunately, this process works too well, and hobbyists end up with rocks and sand that is totally lacking the life we spend so much money trying to get into our systems. Think about it like this. Why pay anywhere from $5 to $12 per pound on live rock that you’re just going to cook anyways? If you’re going to buy the expensive stuff, try to keep that stuff alive.