On Mon, 30 Apr 2007 11:52:03 GMT, "Alan Holmes" & others wrote:
Fresh tap water is harmful to fish.
Never bothered mine, I always left the water for a few days before
introducing the fish.

That is ok if your water company uses chlorine, it will de-gas ok in
that time,
however a new(ish) treatment is chloramine (which was probably not
much used in 'Alans time' by the companies and is less used by them
today than in the '80s and '90s) and that takes much longer to
dissociate and disperse and is especially harmful to gills.

Which is why you put dechlorinator in it, or let it stand for several
hours before adding it if you have a container big enough, as any
sensible fishkeeper knows.

No such things as declorinators 50 years ago.

Yes there was, but it was known as 'hypo' as used by photographers,
also known as sodium thiosulphate, but even that name has had a modern
politically correct name change.
Sodium thiosulphate is much cheaper than the "de-chlorinater" sold to
fishkeepers who dont know any better.