How to Clear Green Pond Water
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.
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).
Has this hub inspired you to build a biological filter for your pond?
Clear water after just 4 days.
By the afternoon of the 3rd 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 4th 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.