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GaryD

Maximise CHOP System Grow Bed Efficiency

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The CHOP (Constant Height One Pump) system of Aquaponics (sometimes referred to as CHIFT PIST) utilises a sump tank.

Since, in the case of a flood and drain system, the sump tank has to be large enough to accommodate fluctuating water levels, you can use a sump tank in such a way that it makes a much more effective contribution to the overall system design.

By using a grow bed (or two) as as a sump, you kill two birds with one stone.

This combo growbed/sump tank can be used in a variety of ways including:

  • A duckweed tank
  • A water garden - for the production of water chestnuts or kangkong (water spinach)
  • A satellite pot garden - support plastic garden pots filled with clay pebbles on house bricks in the tank. As the overhead grow beds flood and drain, the water level in the grow/sump tank (and the pots sitting on the house bricks) will ebb and flow, too.
  • A fingerling tank
  • A combination of these.

There are aquaponics kits that feature a sump tank of the type that I've described - see 1st diagram below.

These can be made much more efficient and productive by simply re-positioning the grow beds relative to the sump tank - see 2nd diagram below.

This is one situation where I recommend the use of a 300mm grow bed.

Caution: Bear the safety of toddlers in mind whenever designing any aquaponics system.

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I guess the only disadvantage Gary is that growbeds at ground level aren't as easy to work with. A lot of people are probably willing to sacrifice efficiency for ease of use.

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Hi Arachdog,

While the diagram shows the sump tank as being on the ground there's no reason why it has to be that way.....so long as it is below the other grow beds enough for them to drain into it. In any case, the sump tank is 300mm deep (it absolutely positively has to be a minimum of 300mm) so it starts off raised anyway.

Gary

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Gary,

when you use a sump are you siphoning the water from the fish tank to the sump? It appears from the diagrams I have seen that the one pump in the CHOP system is in the sump.

I have never used a sump because I prefer to have the pump in the centre of the fish tank to remove solid waste. I then pump to a raised barrel which is a swirl filter that removes solids before water goes to the GB's.

As water is always flowing through the system, tank water height has never been an issue for me. so while I can see the reasons for the CHOP system, the main disadvantage would seem to be getting the waste out of the fish tank without a pump.

Dave

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Huh? I just looked at the two diagrams again. Why would you have the cement blocks in the sump tank at all? Any reason for this? Your suggestion Gary just seems like common sense. How could you move the sump tank with the blocks in it anyway?

dave

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Hi Dave,

when you use a sump are you siphoning the water from the fish tank to the sump? It appears from the diagrams I have seen that the one pump in the CHOP system is in the sump.

In a CHOP system the water flows from the fish tank through the growing systems and then into a sump. The pump (located in the sump), moves the water back into the fish tank.

I have never used a sump because I prefer to have the pump in the centre of the fish tank to remove solid waste. I then pump to a raised barrel which is a swirl filter that removes solids before water goes to the GB's.

Part of the rationale for a CHOP system is that you avoid churning the solids up and that makes them easier to remove. You can install a mechanical filter between the fish tank and the growing systems.

As water is always flowing through the system, tank water height has never been an issue for me. so while I can see the reasons for the CHOP system, the main disadvantage would seem to be getting the waste out of the fish tank without a pump.

In practice, it's not the disadvantage that it appears - it actually works. CHOP also allows for much greater flexibility in the placement of growing systems......while still only requiring one pump. Having the grow beds drain back into the fish tank is not always practical for some people.

CHOP is also a better proposition for me because it accommodates a trickling bio-filter immediately before the fish tank. The location of the bio-filter ensures that it operates with minimal solids loading and the water returning to the fish tank is well-aerated.......and I can disconnect the fish system from the grow beds as required.

Huh? I just looked at the two diagrams again. Why would you have the cement blocks in the sump tank at all?

That's the way it was designed and offered......see here.

Your suggestion Gary just seems like common sense.

I think so, too.

How could you move the sump tank with the blocks in it anyway?

I guess you'd have to unload the grow beds and re-position them outside of the sump tank. In so doing, you improve functionality quite considerably.

Gary

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Part of the rationale for a CHOP system is that you avoid churning the solids up and that makes them easier to remove. You can install a mechanical filter between the fish tank and the growing systems.

That kind of clashes with your suggestion of putting fingerlings in the sump.

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My fish tanks stand about 4 feet off the ground. I think if I had a much higher fish tank with more volume I would be tempted to try this arrangement. I don't think there would be much advantage in my present system. I still use one pump in the fishtank. I get very good water quality and there is minimal movement of water up or down in the fish tanks. Safety protection is covered by using a pump with a built in float switch so if water level drops due to a leaking grow bed or filter, then the pump will stop and leave enough water for fish to survive.

Thanks for the clear explanation Gary. I can see that the sump is conveniently placed under the growbeds but that may not suit every one. A better solution would be a frame that supports the growbeds and allows the sump to slide out when needed for cleaning without having to dismantle everything.

dave

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Hi Arachdog,

That kind of clashes with your suggestion of putting fingerlings in the sump.

Using the sump tank as a fingerling tank would not be my preferred option and would rank behind using it as a duckweed tank or a water garden......or a flood and drain grow bed using pots filled with media......for my purposes.

Dave.....

Thanks for the clear explanation Gary. I can see that the sump is conveniently placed under the growbeds but that may not suit every one. A better solution would be a frame that supports the growbeds and allows the sump to slide out when needed for cleaning without having to dismantle everything.

An even more productive one, as I've suggested, would be to set the sump tank up as part of the growing system - for a substantial increase in growing space for no added cost. All it would require would be to move the existing grow beds a couple of feet either way.

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Hi Dufflight,

A sump can also be an added bio filter for increasing the stocking densities of a system. My new system uses one.

How does that work? Any pictures?

Gary

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Since, in the case of a flood and drain system, the sump tank has to be large enough to accommodate fluctuating water levels, you can use a sump tank in such a way that it makes a much more effective contribution to the overall system design.

The funny thing is I read the post originally, then yesterday I went to put my sump in and strugged with the fact that if I put it under my bed, it makes part of the bed slightly in accessible. The Sump I have is an old fibreglass spa bath in a triangular shape and as I have to dig it in I was slightly concerned about weakening the footings of my grow bed as well.

I then thought about this idea and might run with it, did a lot of reading on DWC last night it might be a good idea.

Caution: Bear the safety of toddlers in mind whenever designing any aquaponics system.

Yer .. I am struggling with this one too.

Anyway .... weekday project. Off Kayak fishing and picnicking today. Will take some photos during the week.

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This is a small one that has a cod in the outer part and the bio filter in the center. Water returns via the center and the PVC has holes at different levels so it keeps working reguardless of the tanks height. No pictures of the new one till I finish hooking it up. But its a larger version.

DSC02152.jpg

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This is a small one that has a cod in the outer part and the bio filter in the center. Water returns via the center and the PVC has holes at different levels so it keeps working reguardless of the tanks height. No pictures of the new one till I finish hooking it up. But its a larger version.

I'm assuming that the PVC pipe is filled with media and, as the level in the sump tank rises and falls, it spend some of its time out of the water (which doesn't matter because you have the line back into the tank feeding into the bio-filter). Is this how it operates?

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Hi Dufflight,

The media is moving so it does not matter what the level is.

OK, I assumed that, when you referred to media you were talking about something like gravel or clay pebbles. It sounds like you're actually talking about a moving bed filter which usually employs manufactured plastic media which is kept churning by the movement of air through the semi-floating media. Am I on the right track?

I've contemplated the use of a bio-filter (filled with oyster shells or clay pebbles) attached to a sump tank before (this is a feature of The Queenslander design) but not quite in the same way you've described......where the sump is in the bio-filter.

I've also used moving bed filters (containing Kaldnes K1 plastic media) but in a stand alone drum rather than as a sump. The manufacturers of K1 claim that the media will process quite high levels of dissolved waste.

And with it running on air stones if there is a power outage the air is on a backup so it still moves the water around. This one was hooked up via constant height to the tank beside it.

Is this where the idea of your airlift comes in......to ensure continuous movement of the water between your sump and fish tank?

I like the idea.

It dispenses with the need for a separate bio-filter container. It also fits in with my preference for a bio-filter immediately before the fish tank.......so that any sedimentary and suspended solids will have already been largely removed thereby optimising the bio-filter performance. It also simplifies the plumbing arrangements.

What media do you use in your device?

While I had planned to use oyster shells or clay pebbles in The Queenslander, I still have 50 litres of Kaldnes K1 (that cost plenty) lying around......so I might give that a whirl.

Oh, by the way, I think it's an excellent way to leverage the effectiveness of a sump tank

Gary

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I'm sure it was a great deal cheaper......particularly if you place no value on the time that it took to cut it up.

Of course, it has nothing like the surface area of manufactured media like Kaldnes K1......which if I recall correctly, cost me about $3 per litre.

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Surface area was not too bad. The cutting up was easy with a guillotine. 5 bits a second ish. And its easier to make up a little more if you need it. $50 per 100mtr roll, 10000 bits cut at 10mm or more if cut smaller. I also like the black so it cuts down on the light penetrating the media.

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That sounds pretty reasonable in terms of cost and effort required. How much media (in litres) do you get from a 100mm roll?

And with it running on air stones if there is a power outage the air is on a backup so it still moves the water around. This one was hooked up via constant height to the tank beside it.

When you referred to be able to still move the water around, are you referring to just in the sump....or does you device function as an airlift to move the water from the sump into the fish tank?

Does this system.....or the one you're about to build.....have growing systems attached? I'm trying to get a picture in my mind of the water flow.

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New system will have 2 stage bio. One in sump and one in a 200ltr drum connected to the main ft. The airlift will move water through the drum 24\7 so power outage will not effect fish.

Growing system is yet to be worked out. Not sure what I'm going to be growing in it. Or will it be used to harvest nutrients for the rest of the garden. I'm allready planing on using the swirl filter on the larger system to run worms in a seperate drum for castings. Do like the idea of dropping all the siphons in gbs in favour of one large siphon in a separate drum.

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According to my calulations surface area is actual good, comparable to bio-balls. However, unless I've made a mistake, even if you don't count the labour, it appears that polypipe is actually more expensive than bioballs. With a 75% packing density, which is what spheres typically pack to, I'm not sure about cylinders. It works out to 565 pieces per litre. Which is only 18L for the full 10000 pieces (which, if your interested, worked out to 7.9m^2 of surface area).

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Hi,

There's some useful reading on bio-filter media......here.

For your interest, the Kaldnes K1 media to which I referred earlier has a surface area of 800 square metres per cubic metre of media.

Gary

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Hi Gary,

I calculated about 450m^2 /m^3 for dufflights polypipe media. Not quite as good as K1 but better than many. But I didn't attempt to account for surface area loss resulting from touching bits of media. Mind you I doubt the K1 manufactures do either. I think it may actually be better than K1 in void fraction and free passage diameter.

So do you know of any Australian suppliers of the so called 'structured packing' written about in the link you provided? I've been looking for something like that for a while now with no luck.

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So do you know of any Australian suppliers of the so called 'structured packing' written about in the link you provided? I've been looking for something like that for a while now with no luck.

Sorry.......I don't. I'd be interested if you do find an Australian distributor. I'd be happy to give it a go.

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