Me personally, I wouldnt add sea water even though I live in flordia and its readily available. You just dont know whats in it.
As far as rock curing, I would say a few days separate from the tank and livestock should be enough to make sure it doesnt spike. You can use a rubbermaid container with a powerhead and heater in it.
I'm also usually overly cautious though so some people may have tried other methods sucessfully too. each tank and each situation is different.