~ janj wrote:
Buy a product that will detox the chlorine. Sodium hypochlorite is the
chemical name. Unless you have chloramines in your water source you'll need
something that will detox chlorine and ammonia, one product name is Amquel.
A few hours will not do it, more like 24-48 hours depending on ppm. Better
is to trickle the water in slowly, or spray it up in the air (chlorine
only) if you can't get or find the chemicals mentioned above. ~ jan

Some water suppliers in the UK use chloramines in their tapwater not
chlorine. I used to age water for aquarium water changes by leaving it
at least 24 hours. I switched to chemical water treatment after I found
out that chloramines were more stable and would take much longer (a
week?) to clear from water naturally. My water company at that time
told me that they used chlorine, but it would be possible that they
would switch to chloramines without notice. I didn't want to discover
that my water company had switched from chlorine to chloramines by
finding that my fish suddenly died and my biological filter was dead as
well.

While I have an aquarium not a pond, I was in a garden centre last
weekend, and noticed a product for dechlorinating (removing heavy
metals and the like) pond water. It was in a spray bottle thing, and
said to use one spray per N litres of water.