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I've got a small wildlife pond which I built back in the autumn, I recently added some hornwort and a lily from my other pond, however the water has turned red.

The hornwort is dying off, and I have noticed this week that there is also a red coating to some large pebbles aswell.

Any ideas folks as to what's causing this?


is the pond clay lined or pond lined it sounds like something is leaching ointo the water column are you sure that the water is red and not rusty orangy red

My large pond has just turned inexplicably red coloured, any ideas why.? We made it larger recently, and it is all made from clay so all natural no wood or other stuff introduced. Mostly koi carp but other fish present. We do have a lot of geese on there this year but have always had many. Really worried it like looks really bad. havent lost any fish yet but very concerned, had it 7 years and never seen it this colour? Would appreciate any help or advice. Many thanks

Last edited: 27 July 2016 19:27:44

Doghouse Riley

Are you able to "trickle change" the water in the pond?

Or is it too large for that to be effective?

Last edited: 27 July 2016 20:09:38


My pond hasn't gone red, but it didn't smell right last tuesday when it was very hot and the water wasn't very clear as it usually is, so I cleaned the filters and done a slow water change overnight and seems ok now.

I think in my case it was due to the sudden jump in temperature. It's been 15-20° for ages then jumped to 30°+ and I think this rapid jump in temperature has shocked the bacterial life in the box filter (which is in the sun most of the day) and possibly poisoned the water.
Sadly I lost a very big koi that I had for nearly 20yrs

Re the original question - was the water greenish before and was there any algae on the pebbles? If there was, then maybe the algae has died and caused the colour change.

Last edited: 27 July 2016 20:56:06


It's too large to change the water , don't have any filters either it's all totally natural. Never happened before


Sounds like a red algae bloom.  Apparently this can be brought in on pond plants but it's probably the recent hot spell which has led to it proliforating.  I would try one of the barley-based products which claim to reduce algae growth without harming wildlife.

Last edited: 27 July 2016 22:14:56

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