's dont fully cure their LR
before putting out for sale. They usually have a large tank or vat for all the live rock they sell and as new shippments come in they just put the new rock in the vat with all the other rock. The end result is a tub or tank that is almost always in a cycle.
Its always good to quarinteen the rock from the store for a 24 hour period in a QT
tank or even a bucket with a powerhead and heater and saltwater. After the 24 hour preiod check for ammonia and nitrite. If either test positive then let the rock sit for another day before testing. If both tests are negitive then you can add it to the tank.
If the rock is only suffering slight dieoff you can add small amounts to an established tank but this is risky as if you add a rock with massive amounts of die off you can cause an ammonia spike in your established tank.