My book on Koi care written by Doc Johnson says that there is not safe
level for Chlorine exposure. Only amounts that are not immediately
lethal. Chlorine does cumulative damage to fish gills.

Cheers.

DD DDD wrote:
She has 7 6 inch fish which seems over kill. She said her secret is a
automatic fill and drain system. A valve opens and puts in tap water
everyday (15%) And the overflow tube waters her garden. She uses no
declor. Is it possible to do this? She has done this for 3 years and
never lost one fish. She has chorine in her tap water but says 15% daily
water change has not harmed her fish and her water is crystal clear.