they will die VERY QUICKLY!!! a terrible idea, i must say (though your intentions are good). chlorine kills EVERYTHING, which is why we put it in pools--to kill bacteria and microscopic organisms...as fish are quite a bit bigger, well, they will die in a BAD way...just cruel, really.
story time. so, i am a chem major doing a summer internship before my senior year. i go around to different bodies of water to kill algae and other plant life. i get to this pond where people swim (lifeguards and all). the head lifeguard--high school dolt says that he thinks MY chemicals are killing the fish. i said i had never been there before, but it is ridiculous nonetheless. i asked if anything stange had happened--no. had they done anything to the pond? he said no...we just started putting chlorine in a couple of weeks ago...i flipped out..."well, you know they put it in pools, so it must be ok." the real shock ofr me is that someone is actually the boss--and he purchased chlorine FOR them.
now, i am not calling you a dolt...just informing you that it is my educated belief that you will have a goldfish genocide on your hands BEFORE the party ends...and it might, in fact, end the party.
go with tons of silver balloons instead--NO CLOWNS! nothing scarier than a clown...but that is another story!