also, if the rock is dried out, it wouldn't have anything in it to add to the ammonia and nitrite levels. If you were using uncured liverock, a good rule of thumb is adding no more than 10% of total pounds at one time (in your case, with your 80 pounds, you could add 8 pounds) to avoid a sp ike in your water chemistry. Again, if the rock is dried out, it wont have anything dying in it to pollute your water, so you'd be fine.