Put the rock in either another tank or rubbermaid tote or bucket with a heater and powerhead. Test for ammonia and nitrites and if there are any the rock is uncured, you will have to let it cure for a few weeks until it reads zero for at least a week, you may have to do water changes to keep the ammonia under 1. Don't put it in your tank until you are sure it's cured, it should smell fresh when done curing.