What Causes Green Pond Water?
Green pond water is caused by an abundance of single-cell creatures known as algae. When their numbers reach epidemic proportions, pond water will become like "pea soup." Although harmless to fish, the water looks unpleasant and completely ruins the enjoyment of keeping fish and aquatic plants.
The other week we had family visiting from Holland. The Dutch know a great deal about water and water quality. To be honest, my green pond water was an embarrassment to me. I made a commitment to get my green pond water clear.
My Experiences With Green Pond Water
Over the last years 40 years or so, I've had several small garden ponds, and green pond water has been an ever present problem. Sometimes I have managed to get the water clear, sometimes not.
Getting the water clear and keeping it that way was somewhat hit or miss.
However, since the advent of the internet and in particular sites such as Wikipedia and YouTube, the amount of information and knowledge available to the amateur pond builder and fish keeper has grown exponentially.
For me, the breakthrough came when I understood fully what green water is and how it can be stopped.
The algae that causes green water cannot be filtered out. It is a micro-organism.
Therefore, it must be starved out.
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Efforts to Clear My Current Pond
In an effort to clear my current pond I did several things.
Firstly, I cleaned out the pre-filter unit attached to the pump and added some "bio-filter" media.
Bio-filter is material designed and manufactured to promote the growth of naturally occurring "good" bacteria.
Secondly, I added an air supply into the pond water with an air pump and air stones.
Thirdly, I added various water plants.
The pond water remained "pea green," much like pea soup. All this effort for no reward was very frustrating.
Nutrients, Algae and "Good" Bacteria
Creating and maintaining clear pond water stems from having a lack of nutrients for the algae to feed on and an abundance of nutrients for pond plants to eat.
The primary sources of nutrients in a small pond will come from fish waste (their excrement) and uneaten fish food that is decaying.
There will be two types of naturally occurring creatures eating these nutrients, algae and "good" bacteria.
Green water means that the algae are being the more successful at colonising the pond water. Whereas clear water indicates that the "good" bacteria have the upper hand.
After finding out the facts about green pond water, I decided to try my hand at some "biological engineering." That is, I wanted to see if I could create an environment that would enable "good" bacteria to proliferate in my pond water, so I set about designing and building biological filters for my pond.
I already had an air supply, a water pump and a pre-filter unit but what else would I need?
After reading articles and watching "how to" videos, I made a list of materials required to complete my bio-filter project:
- 50' Plastic pipe with joints and hose clips.
- A ball valve.
- Plastic containers (around 5 to 10 gallons each).
- Filter media (scrubber pads from the dollar store).
- A source (an existing colony) of "good" bacteria.
The Basic Concept
The basic concept behind my plan was to create two colonies of "good" bacteria, living within plastic containers external to the main body of pond water. The scrubber pads would provide the right kind of "home" for the bacteria to colonise.
The pump, tubing and joints would enable me to create a flow of water between the plastic containers and the pond.
Construction Begins With Dismal Failure
My first attempts at setting up the plastic containers with water flow to and from the pond were a dismal failure. At one point I thought I might have to abandon the project altogether.
I couldn't get any of the joints in the pipe work to seal properly. Water wasn't just leaking here and there, it was spewing from every single connection. The joints to and from the plastic containers were so ineffective I don't want to talk about them any further.
At the end of that first day I sat in back yard looking at all the materials scattered across the floor and said to myself, "what a complete waste of my time and hard-earned money!"
I went to sleep that night hoping I'd have some kind of "creative-genius" breakthrough in my thinking.
By the next morning, I had some ideas to work with.
The Second Day of Construction
During the second day of construction, my hopes were raised that I might get something that worked, even if it didn't look pretty. My plans were based on a single 30-gallon plastic tote.
Trying to get water flowing from the bottom to the top of the container had been causing many problems with leaks at the joints. By reversing the water flow I could do away with the connections to and from the container. Pipe from the pump in at the top, holes in the side of the container at the bottom would allow the water to just pour back into the pond.
I filled the container with scrubber pads to provide an environment for the "good" bacteria to live in.
I had some existing "bio-media" from the pre-filter, so I put that in the middle of the scrubber pads and set the water flowing.
That night I went to bed wondering if the morning would bring success or failure. By the morning, I knew that the colour and clarity of the water would soon let me know if I were on the right track or not.
The Third Day Brings a Breakthrough!
The morning of the third day of construction brought great excitement in our house. The pond water that had been pea green was now clearing, we could see about 3" (75mm) down into the pond. To get the water this clear in just 12 hours was nothing short of miraculous. Also during the night I had come up with a way to create water flow to and from two containers without water leaking all over the back yard.
I would put all pipe joints within the confines of the pond.
Here is the sequence of construction I used:
- Pre-filter unit.
- "Tee" joint.
- Hose to right-hand side container.
- Hose to left-hand side container with ball valve (to balance water flow).
Clear Water After Just Four Days
By the afternoon of the third day, construction was complete. Any leaks in the joints didn't matter as they were all under water in the pond.
The ball valve was regulating the water flow correctly between the two containers.
When we got up the morning of the fourth day we had clear pond water. The bottom of the pond was clearly visible.
The two colonies of "good" bacteria living in the scrubber pads had starved the algae to death.
This is how I cleared my green pond water.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
freeradicalsteve (author) on January 25, 2018:
John Dove on November 03, 2017:
Hi Free Radical--
Thanks for describing your experience, good and bad. I wonder what the name of the "good bacteria" that you nurture with your setup?
Saravanth on July 29, 2017:
Hi sorry to bother u again i am just putting a detailed account of my encounter. Just removed soil from my pond and weighed down the water plants they sort of died and are just leafing up. After replanting water was crystal clear later experienced pea soup condition after reading ur blog added a home made fliter pump and fountain which were not there earlier just after 2 days peasoup condition is just popping up not able to see the bottom. I think the fountain provides aeration. Pls help on the various methods. Just didnt add bacteria could u pls elaborate on that have zero idea on starting a colony pls help. Ty in advance...
Saravanth on July 29, 2017:
From where and how to get the good bacteria? pls do elaborate...
Haggis on June 04, 2017:
That's brilliant my brain has now gone into building and design mode I ty I will let hub know how it goes. Just had idea while typing my plasterers bath is perfect start
FishkillerOMG on April 19, 2017:
I've tried everything the fish store has told me. I'm going to try almost all natural can't hurt. I'm going to try the bio balls and making a small pre-tank with good bacteria. Wish me luck all ... I just really love goldfish ponds and can't get this one to cycle properly.
Rob on February 14, 2017:
I have read your article several times and I gave the exact same problem with my fish pond. I built a filter as you described and also had reasonable success. The pond is cleaner and I can see my fish now, however I reckon I can do better. Question.... the "sludge" in container after two weeks is gross. I realise it is "working" for me but ask if I should remove some of sludge. Thinking maybe clean out about 80% and let it start again. What do you think? Also not sure where to get and exactly what bio balls are.
Bradford on December 16, 2016:
Green water algae can be removed by controlling light conditions. 1 week of no direct sunlight will kill it all. But the dead algae settles at bottom of pond and must be removed or filtered otherwise water goes bad real fast.
Other way to get rid of this I believe is to add some potting soil to the water. Green algae does not like that. Soil must be washed to remove fine particles and extra chemicals only. The heavy bigger particles will settle down fast and can be added to the pond. I would suggest first trying this in a small tank as experiment before taking it to the pond.
wayne, Kent uk on May 22, 2016:
Thankyou for sharing , I've had nothing but problems with my pond since a changed my small filter to a larger filter
It's completely pea green
This has given me some ideas to add to the new pond when I re-locate it bigger and deeper in the garden
Rishim78 on May 22, 2014:
I just made a pond for my turtly 2 weeks now. The green water is killing me. Dont' have lots of money to spend. I do a a good pump and a aquascape falls.
I was not able to see the pics you put up. Some show and some did not.
So your fast result was because you already had "good" bacteria from the bio balls? I would like to see a pic of the overall setup
Christian on May 06, 2014:
Great post, I am not into this, to be honest, my interests is into lawn mainly (I also run http://www.247lawn.com) but your article intrigued me and I actually ended up learning a few things so thanks :-)
marion langley from The Study on June 26, 2013:
Great Hub, easy to read the writing and follow the pictures! I love how you positioned the bio filter to spill into the pond, visually appealing. I've been doing research on aquaponics and they rely a great deal on biofilters, ultraviolet light, and shade to keep algae away. While they do not harm the fish they do compete with them for oxygen if i'm reading things correctly. Never saw scrubber sponges used as media - what a practical idea. Thanks for writing!
moonlake from America on June 17, 2013:
Congrats on HOTD. Great information. I will come back to it if we ever get the time to get our pond in. Voted up.
Rebecca Mealey from Northeastern Georgia, USA on June 17, 2013:
No doubt this will be of help to many. Great job and congrats.
CZCZCZ from Oregon on June 17, 2013:
Well written and detailed hub. Lots of good information!
rose-the planner from Toronto, Ontario-Canada on June 17, 2013:
No wonder your article made it to HOTD! This was very informative and interesting and your images were awesome. Thank you for sharing and congratulations. (Voted Up)
freeradicalsteve (author) on June 17, 2013:
Many thanks to you all for reading my hub and your comments and feedback. This experience has been a great encouragement to me.
Tim Nichol from Me to You on June 17, 2013:
You're so right, Steve. Algae is the bane of pond-keeping. Good work. I'm using a fancy Laguna pond filter with an ultraviolet lamp, which kills the algae on its way through. So you end up with dead algae on the bottom of the pond, instead of floating around, creating that pea soup look. And of course there is regular cleaning of the filters. Oh well.
To minimize the algae proliferation, the pond should be in a shaded area, with not much sunlight. This is of course difficult in the spring, with no leaves on the trees. Lots of good info online, if you go to the professional pond & aquarium sites. YouTube videos are more often than not, bogus advice from people who don't know what they're doing. Beware.
Mr Archer from Missouri on June 17, 2013:
Over the years we have built ponds in several homes and I know exactly what you are saying! it can be a challenge to maintain these habitats but they are such a blessing to sit and watch, and just hear the burbling waters. Great job and a hearty well done!
Comfort Babatola from Bonaire, GA, USA on June 17, 2013:
Nice hub with great tips for a clear green pond. I would love to have a pond, but I'm not ready for the work involved. Maybe get the pros to do all the work.
Thanks for a great hub, and congrats on the HOTD award.
Lynsey Hart from Lanarkshire on June 17, 2013:
Well done on HOTD . The results look amazing! Clear water achieved... I think maricar can perhaps see the residue of green which is on the stones, rather than in the water itself. You could always get some algae eaters for that?
Cecil Wilde from Melbourne, Australia on June 17, 2013:
This is great! When we had a pond it was perpetually so green you could barely see the (sizable!) fish we had swimming around in it. Now I know how to clear up the water if I get energetic enough to put another one in.
mjkearn on June 17, 2013:
Hi Steve and welcome to HP.
Congratulations on your HOTD. Great hub, excellent pics and fabulous advice.
How are you at DIY Swimming Pools and filtration. I've got the JCB, Mixer and a large chalked rectangle on the ground, LOL.
Have a great day.
Voted up and shared.
Maricar on June 17, 2013:
the last pic of the pond doesn't look clear.. sorry ...just my opinion.. my husband is a water application chemist so I saw a lot of really clear waters...
However you did a great job on your hub!
freeradicalsteve (author) on June 03, 2013:
I believe the algae that turns pond water green is harmless to fish. There are various do's and don'ts with pond building, mainly around location. I have found that the people who sell pond plants are very helpful on building ponds as their livelihood depends on it. Moore's Water Gardens in Port Stanley have a lot of info.
Zsuzsy Bee from Ontario/Canada on June 03, 2013:
Does the algae bother the fish? I'm just doing all my homework because I would like to add a pond into the garden.
Great hub along with great pictures. Voted up and useful.