I guess what I would do in your situation is do a water change to
dilute any possible contaminants in the pond. As far as fish are
concerned, I have a pond that is a little smaller than yours and I put
the 10 cent feeder goldfish (regular and comets) into the pond and they
have done well. I probably have 50 in the pond. In a year there were
some that were over six inches long and there are some pretty cool
looking ones (especially for the price). I tend to think that they
would be hardier than the fancies so I would recommend adding the
fancies after the pond has been set up a while when conditions are more
stable. Let me know if you have any other questions.
James