Hi Adrian
You're lucky to be able to do part water changes.
Up here in Edinburgh ( and quite a few other places in the U.K.) the water board (Scottish Water) have started using a water treatment called chlorimate . It's toxic to fish and amphibians. If I want to do top ups I have to use a commercial product to neutralise the chlorimate.
It's too expensive to even consider a water change in my 2000 gallon pond. I previously was able to trickle feed 24 hours a day and the water quality was so good that my Orfe bred three years in a row. Try catching 100 or so Orfe fry and try finding a home for them!
Best Wishes
Gogs
Posted on Feb 19, 2006, 11:06 AM from IP address 85.210.40.106