Did you retest for ammonia? I wouldn't expect the ammonia to be "off the scale" only after 3 days, even if you had stuff dying off from the rock.
If the shipment was just received at the LFS
, that implies it spent some time out of water, correct? If so, then you'll see a little bit of die off of both bacteria and critters depending on how long it was out of water - even if it was "fully cured" before it was shipped to your LFS
. You might see a little cycle, or a big one.
Sounds like you're going to have at least a little cycle, so I wouldn't do any water changes at this point. Keep testing to see where you're at in the cycle, and do a big water change at the end of the cycle - when your ammonia and nitrites are back to zero.