I think what had happened was that during the summer when I made it (last year that is) I had accidentally run a load of tap water into the pond when emptying a big paddling pool onto the grass nearby.

So I bit the bullet and changed the water.

But…..and this is the but, I was pretty confident that there wouldn’t be any other sources of polllutants around the pond – particularly no bare soil to wash in, and of course the pond had no sediments to speak of at that point (and actually I removed what little there was anyway). Also I can see that you’re keeping fish – which will make the water quality management a bit more more difficult. There’s nothing wrong with fish, of course (I say that because lots of people over here say fish and wildlife don’t mix) but it is more difficult to maintain water quality, in a way that will keep algal growth under control in relatively small ponds, when you have fish.

So if you were to do a complete water change you’d need to remove sediments too, and be confident that there weren’t other significant sources of nutrients that could run into the pond too – I think in the garden the main risk will be from soil getting into the pond one way or another. But given that you’re keeping fish, and maybe feeding them, it might not be worth the trouble because you’ll soon be re-supplying nutrients just in the normal course of looking after your fish.

So because we’re all still learning about these clean water ponds – and even though everything says – yes, clean water is key – I’m reluctant to say – ‘just go ahead, it’s absolutely the right thing to do’ because so far we don’t have very much practical evidence of how well water changes work.

It would be interesting to know a bit more about the set up of your pond – water source, surroundings and so on.