Replacing pond liner - seeking advice

(The message has also been posted in the "rec.ponds.moderated" group.)

We've had our house for about six months now and are at last getting
around to replacing the leaky pond liner. With the pond, we inherited
about 14 small-medium gold fish, along with one quite large koi carp.
The pond itself will be about a 10ft x 8ft oval, with varying shelves
and depths - the deepest being about 1.5m.

I've read up on the subject and (plan in hand) am pretty comfortable
with the actual physical design/construction process. What I have
read conflicting information about is how long to leave the water to
settle until putting the fish back in?

The local pond centre suggests we keep the fish in a large barrell
during the changeover and reuse as much of the old pond water as
possible. So...we won't be entirely using tap water (about half-and-
half), but some sources have said we should leave it a couple of days
for the water to settle, and others have said upto six weeks!

Can anyone give a bit of advice?

Many thanks,

Tim