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Green water in my new pond

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  • Regular Member

Hi :)

I set up my new pond about a month and a half ago, seeding my new pond filter with bacteria from my 2 tank sponge filters and waited 4 weeks before transferring my fish from their tank.

Water parameters are perfect. I have 2 apple snails, 2 small lionheads, 3 small orandas and 2 medium sized orandas in 800ltrs.

Over the last 2 weeks the water has progressively gotten greener and now I can't see very far into the water. I know green water is okay for the fish and I've got lots of surface aeration adequately oxygenating the pond, so the problem for me is that I can't see my fish.

The pond gets full afternoon sun and I can't move it elsewhere. There is lots of surface cover with Azolla and Duckweed and I'll be adding lilies and some other plants soon.

What I want to know is, is this a stage common with newly established ponds and can I expect to see the green water go away when the weather cools down and the aspect changes in Autumn/Winter? The pond will not get the same amount of sun in the cooler months as it does now (mid summer in Australia).

I don't want to get a uv sterilizer or to use chemicals. I'd just like to know if others with ponds have gone through this stage and seen the green water go away by itself?

Can someone also explain for me what happens in the process of pond establishment/settling that causes the green water and what makes it go away?

Thanks heaps! :)

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Yes, it is common for new ponds to go through a green stage.  It is apparently caused by the green algae outgrowing the nitrifying bacteria/archaea.  Often it goes away on its own, but it can take a long time.  It has little to do with sun unless the alternative is total darkness.


My guess as to what happened is that you seeded your filter without any fish in the pond to feed them ammonia, so the nitrifiers did not grow.  They just sat there waiting for food.  Green algae need little besides water and sunlight to grow, so they established themselves in the pond at a population that was below what it takes to turn the water green.  When you added fish, the green algae gobbled the ammonia and grew like crazy.  


For future information, what you should have done is set up the pond and filter and add one (small) fish.  One fish in an 800 l pond will not produce enough ammonia to hurt itself, but it will feed a seed population of nitrifiers.  After a week, if the ammonia and nitrite levels are zero, add a second fish.  Repeat this process until all of the fish are in the pond.


Give me a little more information and I can help you handle the problem.


Are you doing any water changes?  If so, how much and how often?


Can you show me a picture of your pond?


What do you have for a filter?  





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  • Regular Member

Hi fishywishy,


I struggled with this until I got a UV light and a powerful new filter. Even then it took a couple of weeks for the green algae to clear. I talk about it here in my Jan 6th blog entry.

You may want to use the UV light as a crutch until the green algae is gone. Then you can turn it off or remove it to get things "natural" again. Some believe that the UV interferes with controlling string algae. Passing water under a UV light really works, I've had clear water ever since adding a filter adapted with it.


Let us know how it goes, whichever way you decide.


What are your reasons for not wanting to use UV?

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I'll give you my reasons for not using a UV filter, which may or may not be the same as Fishywishy's.   Basically, a UV filter kills all of the planktonic microbes.  From my way of thinking, this is not compatible with developing a stable and complex ecosystem.  That doesn't mean you can't have a healthy pond with a UV filter.


There is however, a risk involved in zapping a very green pond with a UV filter.  If the pond is chronically green or is a new pond in the green stage you have a very small population of nitrifying bacteria/archaea.  It is the green algae that are removing the ammonia.  Kill all of the green algae, and you eliminate the critters that have been removing ammonia.  The dead green algae will rot, releasing more ammonia,  so the situation can become dangerous to fish.

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  • 3 weeks later...
  • Regular Member

My green water did not go away on its own, it actually got worse in cooler months with lower light...I didn't want to use chemicals or a UV sterilizer either so I added a bog filter to it, and on the advice of shakaho increased the oxygen levels in the water by installing a venturi injector and its been literally crystal clear since.  I also have some very healthy herbs growing out of the bog :)


I purchased the venturi injector from a local koi shop for $2.50 and the bog filter minus plants cost about $15 to make.  Much, much cheaper option than a UV sterilizer.  I've also not really had to do any maintenance to the pond since...its pretty much become self sustaining aside from having to vacuum it and provide top off.

Edited by Reds12
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