Help! Goldfish are Dying in New Pond

I recently put a new pond in our back yard. It is 8' long X 5' Wide at
the longest points and 22" deep. I'm bordering Zone 5 and Zone 6. I'm
figuring it's about 450 Gallon give or take. We filled the pond about
2 1/2 weeks ago and we have not added plants yet.
We have a 750 gph pump with fountain and also a waterfall. After 2
weeks we were told we should add a few goldfish to help with
misquitoes. (we were not planning to use it for fish, just plants
originally) Anyway......after the pond had been filled for 2 weeks we
added recomended amounts of Chlorine/Chloramine Neutralizer and Some
Algae Preventor to the pond and then went to the fish store we always
deal with for our Aquarium. We never really had any problems with the
fish we bought from them and they are highly recomended. We picked up
6 fancy goldfish and I floated them for about 45 minutes along with
adding some pond water every 15 minutes before we released them into
the pond. On the 2nd day we lost 2 goldfish and one more on the 3rd
day. Of the 3 we have left it looks like another might be dying. I
checked the PH level and it was 6.5 (a little low, but I don't think
that was causing the death) The Nitrate levels were Perfect. I don't
have a chlorine tester yet but I did add the chlorine neutralizer
before adding the fish. Both chemicals that were added to the pond
said they were fish/plant safe. Someone said I should put in some pond
salt? I didn't think I needed salt for goldfish.....but could this be
my problem? Did I miss anything else?

Thanks in advance,
Mike