Help needed with pond design

Here you can find some good examples of Airlift powered ponds.

Help needed with pond design

Postby Volker » Sun 23 Oct 2016, 13:10:48

Hi all, I am a new member to this forum, and require some assistance with pond design.
I came across your web site and am really fascinated at how well the airlift system seems to work, and how much saving can be achieved. Electricity costs have quadrupled in South Africa over the last few years.

I recently moved into a new house and "inherited" a pond. It holds 5000 liter (too small I know for serious koi keeping), with depth 65 cm. there is no bottom drain installed. Currently 50 mm piping leading out of

The filter room is below pond level, which would make gravity filtration possible.return height to pond level is 170 cm.

Current filtration system is totally outdated.... Old type pool sand filter is first mechanical filtration, goes to bio-filter, then to uv light, return to pond. All plumbing on 50 mm piping.... Filtration done by pool pump.... Which is extremely expensive..!!!!

Would an airlift system work?... I realize that my pond construction is not ideal,....but nevertheless want to optimize the existing system as much as possible. Can I keep the 50 mm piping as intake pipe?... The pre-filter chambers I plan to get are built with 50 mm piping diameters.
From the info on the site, I have learned that the airlift system can run the pre-filters ( plan to install 2 separate filters with brushes) for now.....lead this to the airlift chamber (in collection tank). What happens to the bio filter and uv light?

I am quite new to the hobby of koi keeping and would really appreciate any imput,,,


Many thanks

Greetings from Cape Town, Volker
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Re: Help needed with pond design

Postby Pssymon » Mon 24 Oct 2016, 2:49:09

Hi Volker, welcome.

First of all, what do you want to keep in the pond?
You say it's about 5000 liters and 65cm deep, that is quite shallow. You could consider digging down to 130cm for example and you would get double that, the pond would be more suitable for Koi that way.

What kind of fish were kept in it previously?

First of all, to answer your question quickly, yes I think Airlift would be a good idea.

You mention the 50mm connections, those will be way too small. So you would have to put larger transits through those filter chambers or add more 50mm transits.

I talked about this with Marc recently, when running the standard type Airlift on a 20w pump, you're going to need two 110mm transits (at least) between every filter chamber. The Airlift needs to have very little resistance to pull all those litres through the filter.
So, you'd need a surface area of PI times the radius square. In this case, 3,14 x 5,5cm square x 2 = 189,97cm square. This is the surface area you need for optimal flow without restriction.
A 50mm transit will have a surface area of 3,14 x 2,5 square = 19,625cm square. So you will need about 189,97 / 19,625 = 9,68... So 10 of those transits between each chamber.

That is not very practical, it's best to use 110mm or more, but bigger transits and pipe quickly become expensive.
You can build a Collector and Airlift and use the filter chambers with smaller or less transits, but in that situation the Airlift will never perform at its full potential.

About your other questions.
A single Airlift will filter your pond with room to spare, even if you would double the volume.
It can run your entire filter, not just prefilters. If the prefilter chamber(s) and bio chamber(s) are linked in series with the Airlift at the end it will work perfectly.

The only thing that you would need to change is the UV unit.
A normal UV unit with a metal or plastic case around it cannot be used as these would restrict the flow too much. You need to use a submersible UV unit which can be placed in a transit pipe or in the Collector.

I was unsure, but did you say your filter chamber (especially the last one) is 170cm below water level? In that case you would not need a Collector as the depth would already be sufficient for the Airlift.
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Re: Help needed with pond design

Postby Volker » Wed 26 Oct 2016, 0:25:19

Hi,
Thanks for your quick reply.
I believe that the previous owner kept goldfish in the pond. Is the pond totally unsuited for koi? The pond receives direct sunlight for only half a day and cold temperatures aren't really an issue in Cape Town. The summers can however get quite warm.
You have provided great detail.....I didn't want to incur the cost of making the pond deeper right now, but reading your reply I think I must rethink this approach.

Best regards
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Re: Help needed with pond design

Postby Pssymon » Thu 27 Oct 2016, 1:21:53

Hi Volker,

I'm not a Koi keeper myself, so I'm not an expert on the exact needs of Koi. The limited depth may be okay for them, but keep in mind that the smaller the pond, the more unstable the water values will be. So you will be limited to a very small number of fish. You could counter this with a big filter and an Airlift providing a high flow rate, but if something goes wrong, like a power outage or keeping one fish too many, you will cross that line where your water becomes toxic very quickly.

Feel free to let us know how you will continue. If you have any questions you can always ask them on the forum.
I'm working on a basic topic about filtration, gravitational filtration and how an Airlift is used. That should be up soon, it took a bit more thinking and fact checking than I had expected.
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