The rock must be cured whether it was "precured" or not. Just pick up a large rubbermaid container and place the rocks in there with some aged saltwater and keep the temp at 80 or so with a few powerheads to create movement. The powerhead can also help remove some of the dieoff. You can scrub in the crevices and on the rocks with a toothbrush to get some of the dieoff off. Make sure not to place the rocks into the main tank until the curing has finished (0 ammonia, 0 nitrite, low nitrate). Good luck!