Uh oh... chlorinated water made it into the tank

[xnmuller]

So while I was away in Vegas (brought home $250) someone topped up the sump with about 3 gallons of tap water. The tank and sump together are about 175 gallons. I do not have any fish or corals yet, the tank was just finishing its cycle from initial setup about 6 weeks ago.

How bad is this, did it kill all my love rock (120 lbs)? Should I do a very large water change or can I just put in some de-chlorinator? Anything else to worry and stress over?

Please help!