As mentioned above If you add fully cured LR or even un-cured LR you will have a problem is this particular situation because the added Bio-load is going to cause a demand on the rock. The fact that rock is cured doesn't mean when put in a tank it is at equilibrium, you loose that balance because you have ammonia, nitrates & nitrites, right away the bacteria on the rock will start growing, multiplying & feeding on the frenzy of available food, this will spike hard enough to possibly kill your entire tank, depending on the condition of the rock & the amount of rock. The people here are trying to help you understand this, don't take the information provided wrong. The first thing any reefer will tell you when starting gout is READ, Read & Read, it take years before you will have enough experience to really understand what is going on & even then you still are learning, so don't take any of this to offense but rather a bunch of friendly people trying to help you!