Water changes in ponds

Mallet wrote: Just a quick question.
Should you do a water change in a 1000+ltr pond and by how much and how often, is it worth keeping a barrel of rain water on hand or just use the garden Hose and tap water ?

I'm not too certain about percentages of water to change in ponds - or how often, maybe more pond-oriented members will comment on this.
All I'll add is that the considered opinion is that the sorts of fish we regularly keep in our ponds (mostly Carp species - or Carp derivatives) seem to do better in harder alkaline conditions so if your tap water is anything like mine this might be the better plan of action.
Having said that, my pond is constantly topped-up (overfilled...) with rain water from the roof of my garden shed and the Koi don't seem to mind - they haven't complained to me, anyway.

Maybe we can get some more informed comments from proper pond people.

John