OK, let me make sure I understand. You had the sand and some base rock and then you added the cured rock. Before you added the cured rock you had
ammonia but no
NO2 or
NO3. Two days after adding the rock you have no nutrients at all.
Since there was an existing
ammonia challenge in the tank I think that this means the
LR did its job and converted it. You could add a cocktail shrimp but since you already had
ammonia I don't think it is necessary. I would probably add a tiny pinch of food every couple of days as a source of food for the bacteria and keep monitoring your tank. Give it the 3-4 weeks and as long as it remains stable I think you are good to go.
I used fully cured rock and sand from a tank that a guy in the area was tearing down and never saw a cycle. I doesn't always happen this way but it is not terribly uncommon.
