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Aquaponics CHOP Mark 2 Operating System

CHOP or Constant Height One Pump has been adapted by Aquaponics enthusiasts around the world now for the last few years since we coined the term. The other variant Chift Pist runs in a similar way. I noticed a problem with water levels whilst working on a small commercial CHOP system we were commissioning just over a year ago. We needed to refine the process for our client, so we came up with a solution that we've been trialling now for over a year.

CHOP 2 Layout
CHOP Mark 2

It runs so beautifully. I’m very excited by it.

I am so certain this is a better way to run your aquaponics system that we have adopted CHOP2 into all our new larger Aquaponics kits that we design and build.

So what is CHOP Mark2 and why should you consider using it?

Operating the old CHOP method water is pumped up from the sump to the fish tank and from the fish tank runs back to the grow bed and sump by gravity. This system works very well but it requires that the grow beds be perfectly level to function properly. With CHOP Mark2 there are a number of advantages.

With CHOP2 the pump sends the water to the grow bed as well as the main fish tank simultaneously. The water from the fish tank and grow beds runs back to the central sump.

It’s kind of like a double loop water flow with the sump as the central mixing point. It works extremely well.

So what are the advantages of modifying your system to CHOP Mark 2?

The main point is that grow beds do not need to be perfectly level to function properly. A crucial point if you are running a number of them on uneven ground and have encountered problems with your auto siphons. Because each grow bed has an independent ball valve, the water flow can be regulated with greater control than gravity fed flow under the old CHOP system.
Recently we commissioned an 18 bed system utilising two of our large commercial fish tanks. To facilitate good water flow we used CHOP Mark 2 together with sequencing valves.

Because each Fish Tank also now has its own ball valve it means water flow to the fish tank/s can now also be regulated as well.

If you need to harvest your fish and control the water depth or do any maintenance at all, you now have complete control to stop water flowing to your main fish tank or even drain it, but not stop the flow to your other grow beds.

More control for the aquaponics enthusiast also means more control over winter temperatures as the mercury plummets.

In colder climes operators can turn off their grow beds at night but still have their main fish tank running as normal. This is a great boost for owners who complained that their grow beds were acting as a heat sink at night, plunging their water temperature down a number of degrees.

A side benefit for users who will modify their system to CHOP Mark 2 is that should they decide to change their system from a gravel based media to floating raft, CHOP Mark 2 will accommodate their design shift.

If a combination media and raft system were to be built, Swirl filters or regular filters can be fitted easily into the fish tank to raft section, then we can allow the rafts to drain back to the sump.

An elegant solution.

But what are the disadvantages of running this system?

The critics will say that the sump pumps half the water back to the fish tank. Surely this can’t be good for the fish, as solids are returned back to the main tank?

Logically this may seem to be the case, but over a year of trialling this system with hundreds of fish we have discovered that the sump itself acts as a settling tank for solids, something that we didn't expect to see and something that has never happened under the old CHOP system.

You will need to clean your sump occasionally as the solids will be noticeable around the sides of the sump. This is a good thing and it is not hard to do.

What about fish nutrients? Aren't you halving the number of fish nutrients by returning the flow back to the main fish tank?

Some may think that the nutrients from the fish tank will be diluted as the sump water is pumped partly back to the fish tank and partly to the grow beds. In just over 12 months of running we see no reduction in nutrient to the grow beds.
Conversely, some may think that the nutrient level may be too high and perhaps there will not be enough filtration or bacterial action because some of the water that has just arrived in the sump from the fish tank will be returned directly back to the fish tank.

We initially felt some of these fears ourselves, but with 12 solid months of field trials behind we see the systems running exceptionally well.

We see CHOP2 as a definite improvement for the Aquaponics community around the world. Come back in 12 months time as see how many users have modified their system to CHOP Mark 2.
People always vote with their feet. They know when they’re onto a good thing.

The next generation of CHOP. CHOP Mark 2

1 Grow beds do not have to be exactly level with each other as they do for CHOP mark 1
2 Flow to the grow beds can more easily be regulated than with a gravity flow.
3 Fish tank can easily be isolated if required for whatever reason. We regularly switch off the fish tank to pump it down to do a fish count or capture and the grow beds are still left running.
4 Grow beds can easily be isolated if winter night time shut down of the flow to the grow beds is required while fish tank still enjoys excellent water exchange.
5 If a combination media and raft system were to be built, swirl filters or regular filters can be fitted easily into the fish tank to raft section then rafts drain back to the sump.

Happy Aquaponics
First Posted on October 27, 2010

Posted By Murray Hallam on 18th December 2011

Updated : 2nd October 2013 | Words : 1063 | Views : 8014 | Comments : 29

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Murray, could some fresh water lobsters (crayfish) be added to the sump to help eliminate solid wastes?

Posted By John Owen on Tuesday 8th November 2016 @ 02:46:47


Hi John,
It is a great idea. I do not know just how well it will work in the sense that crayfish are difficult to manage. The fight and are great escape artists. I will be keen to hear from you how the experiment turns out.

Posted By Murray on Tuesday 8th November 2016 @ 02:46:47


I was wondering if there was a possibility of the sump overflowing.

Posted By tony trifilo on Sunday 24th April 2016 @ 12:14:26


Hi Tony,
Only if it is too small. Good design will make sure that the sump can hold all the water that will flow to it should everything come to a stop.
I hope this helps.

Posted By Murray on Sunday 24th April 2016 @ 12:14:26


New to all this, how can I incorporate a grow bed specifically to grow duckweed?

Posted By Shawn Paul on Monday 10th August 2015 @ 00:57:48


Just have it off to the side where convenient and run the water from the system in one and out the other. A very slow flow rate works best.

I hope this is helpful.


Posted By Murray on Monday 10th August 2015 @ 00:57:48


problem of this CHOPmK2 system:
part of the water (probably the biggest part) is going back to the fish unfiltered, with part of the solids in it. The bacteria on these solids consume oxygen, in competition with the fish. There will be nitrite buildup in the system, toxic to the fish.
solution: put a biofilter (i.e. a pond filter) on top of the fish tank.
Clean the mats in this filter regularily in a bucket.
Serve the cleaning water to the growbed or to plants in your garden

please explain the CHOP acronym: Constant Height O??? P(ump?)

Posted By Frank De Block-Burij on Friday 27th March 2015 @ 08:24:43


Hi Frank,
All your comments may appear to make sense but the fact of the matter is it works extremely well. There is no nitrite buildup...at all. The additional consumption of oxygen might sound plausible but once again the reality is there is no oxygen depletion in the system. A large proportion of the water carrying suspended solids goes off to the media beds directly or via a swirl filter or a filter system of preference. The small proportion that returns adds no more solids to the tank but is mixed with filtered water that is also returning to the FT from the collection sump. The volume of suspended solids in the FT is always being reduced and balanced.
There are literally thousands of CHOP systems operating very successfully around the world.
The acronym stands for = Constant Height One Pump.

Posted By Murray on Friday 27th March 2015 @ 08:24:43


Hi I just came across you diagram and although I dont know anything about this... I was wondering what stops the flow from the fish tank if the power fails?

Posted By kev on Sunday 22nd March 2015 @ 03:19:53


The water just stops. It is not a siphon.

Posted By Murray on Sunday 22nd March 2015 @ 03:19:53


excellent question, Kev
Murray has already correctly replied that this CHOPmK2 setup is not a siphon,
but I think he should have elaborated on this and further explained:
it is not a siphon thanks to the tee
(in the diagram left of the sign which says "Water by gravity to sump").
This tee (open at the top) will break any siphon action
and the level in the fish tank will stay the same
but let's dig a little deeper into what happens when power fails
in my previous remark (two years ago)
I said that it is not a good idea
to return part of the water back to the fish tank, totally unfiltered, with solids
Murray dismissed my remarks as irrelevant
when power fails, the real competition for the available oxygen starts
and the fish will die much sooner than the bacteria
fast solids removal and biofiltration is extremely important

Posted By Frank De Block-Burij on Sunday 22nd March 2015 @ 03:19:53


also what happens if the pump goes out in the sump tank. Or does that stop the feed from the Fish tank. Im just getting educated on the different systems and what i am going to use.

Posted By steve on Monday 9th February 2015 @ 22:06:50


If the pump in the sump stops then all the water flow will stop soon after.

Posted By Murray on Monday 9th February 2015 @ 22:06:50


Im running 2 250 gal FT can i gravity feed them in to 1 250 gal tank? Also when first setting up the system, the Ft is filled with water and the gravity feed starts. Do i need to add water to the Sump bed and or grow beds? Thanks in Advance Steve

Posted By steve on Monday 9th February 2015 @ 22:03:16


Hi Steve, Add water to the sump usually. The sump is where the pump is so the pump will move the water around the system until it is all in balance.

Posted By Murray on Monday 9th February 2015 @ 22:03:16


Murray, I am in the process of setting up a Chop2 system with a 2300 litre fish tank, 6 grow beds and 3 sumps. Could you tell me how often the fish tank water needs to be cycled per day? i.e. how much water needs to go to the grow beds and how much to the fish tank for optimum performance?

Posted By veganfoodpreparationaul Lamb on Thursday 20th June 2013 @ 11:28:55


Aim for complete water change every hour. In reality a water change through the tank every two hours is good.

Posted By Murray on Thursday 20th June 2013 @ 11:28:55


Hi Murray, I am starting to build a Chop2Mk2 system similar to your plans. If i was to fit it with 2 pumps in the sump, what size do you recommend? Stuart

Posted By Stuart Lord on Thursday 30th May 2013 @ 10:39:15


Hi Stuart, Have 2 the same as recommended in the plans. The idea of two is not to run two, but to have one ready for immediate service should the one in use fail.

Posted By Murray on Thursday 30th May 2013 @ 10:39:15


hi Murray,
Do you think it would be Ok to use a IBC tote that held water based primer paint for a chop mark2?

Posted By arrow dryden on Wednesday 20th June 2012 @ 01:38:02


Give it a good wash out and it should be fine.

Posted By Murray on Wednesday 20th June 2012 @ 01:38:02


What about using Pneumatic? All pumps and valves are air operated, you just have one motor on your compressor. All valve are 24vdc or 12vdc, if you have a power outage your backup is a gas powered compressor.

Posted By Jon on Monday 20th February 2012 @ 21:24:34


Hellu Murray,

I just recently joined your blog. I live in Belgium NorthWest Europe . On the momen temperature at night can be -15 decrees celsius. I have some questions, probably some are real stupid beginners questions.
Do you know of anyone here in Belgium or the Netherlands who are doing Aquaponics?
Anyway, i'm planning to buils a CHOPmark2 system with 3 IBC in a small greenhouse in the garden of our community.
1 question on this CHOP2 system: 1000 liter fishtank 3x approx. 400l growbeds and
say only a 500 liters max in the sump.I'm fuzzeling about the amounth of water in the system. When the sump is empty my growbeds are not filled with water yet, or am i wrong? I could fill them on turn but then i need a special valve. I don't want that! I could fill them in different levels so they drain one after another. As you can see i don't see it clear. If al my growbeds are draining at the same time my sump could overflow. Can you give some more insights on this. How big does the sump needs to be?
Ofcourse if i use plain pebbles riverstones i need les water then when i use the expanded clay beads (her it is called Argex).

Posted By Matijn Goossens on Thursday 9th February 2012 @ 15:19:58


Hi Matign,
If you are using auto siphons, it is rare that they will all dump at the same time. The grow bed capacity is about one third of water when it is fill, so that is two thirds gravel and one third water. The sump needs to be able to hold all the water if by chance all the grow beds dump at the same time, plus a bit more to make sure the pump is covered and working. I hope this is helpful to you.

Posted By Murray on Thursday 9th February 2012 @ 15:19:58


Hi Murray,
Yes, dc pumps are a huge challenge. I have stuck with 12V primarily because of the classic trade-off necessity. Each gain comes at a cost. I am trialling a marine bilge pump that is supposed to be suitable for continuous use. Keeping current draw to an acceptable level has necessitated a slightly smaller output volume. It limits the system to fairly level ground (minimal head) and short distances, but so far seems to be working very well.

Posted By Garry on Monday 6th February 2012 @ 23:22:19


Hi Murray,
This is my first post although I have followed your work with interest for several years now.

I have been successfully running a system very similar to CHOP2 since 2007 (original design by Martin O'Dee) at my school here in Coffs Harbour. One issue not mentioned so far that needs to be considered is that pumping output must be shared between the fish tanks and grow beds. Therefore the pump output needs to be considered carefully. If output is insufficient, problems with water exchange in the fish tanks could lead to critical parameter issues such as oxygen or even ammonia spikes following feeding (depending on stocking density). Basically, a CHOP2-type system may need a higher output pump, with associated running costs.

I am currently trialling a 12 volt, uninterruptable supply system for use in a food security project our school is developing in Bali. Because of the limitations on pump output (primarily because of current demand), I am using the single-direction flow (sump-to-tank; and gravity from tank-to-grow bed-to sump) in order to maintain adequate water exchange in the fish tanks.

One other thing to consider is the capacity of the sump in the event that one section is shut down for harvesting or maintenance etc. The sump needs to be of a sufficiently large capacity to provide for a change in water level in the event of changing input and/or output flows. In my system the sump is not quite big enough and I can run it dry if reducing input flow without carefully adjusting outputs.

Just some thoughts for consideration...

Posted By Garry on Monday 6th February 2012 @ 22:51:58


Hi Garry,
Excellent post, thanks for your input.
I tend to oversize my pumps a little anyway. It is always in tension, the balance between running costs and having a good water flow. We have gone through several pump down-sizings and the having gone a bit too far', up-size again. We are still to identify the perfect pump. ( the perfect pump would be no pump) I feel that a timer system is best where power supply/continuity is at a minimum. We have identified some really good quality timers and we are building a trial system soon to go down that path yet again to see if we can tweek some power consumption improvements in that area. Our backup system has just been rebuilt and we have gone over to 24 vdc. It is much more stable than 12 vdc especially if sending the DC current any distance. Once again the pump is the weakness. Finding a 24 v economical DC pump that is rated for continuous operation and does not draw down too many amps is a challenge.
Your comments re the sump. We find it must be capable of holding all the water from the beds if they all dump at the same time....and then some.

Posted By Murray on Monday 6th February 2012 @ 22:51:58


Murray, I have been running this system for 18 months. The only issue I have had is the size and shape of my sump. I used 55 gal plastic drums and the water flow is high desturbing the settling solids. My solution was a stainless steal 100 micron screen. I also covered the pump with a 12 " net pot and covered the net pot with hydrotone (clay balls). 6 months of trouble free running and counting...

Posted By Chris Jones on Monday 6th February 2012 @ 22:25:49


Hi Chris, That is great. Yes CHOP 2 works really well. You are so right, the sump does need to be big enough. I use rectangular sumps in almost all of my projects and the very fine solid material tends to gather in the corners for fairly easy removal.

Posted By Murray on Monday 6th February 2012 @ 22:25:49


Hi Murray,
I have a CHOP system, with the beds at different levels, but I approached the issue of equal flow separation from a different perspective as I work for Hydraulic and Civil Engineers. In their field the "relative level" of outlets is significant. I applied this principle to my system where the flow is gravity fed from the fish tank to the swirl filter, and then to the beds. These return pipes to the beds are on the ground. The return elbows are at the same "relative level" (using a dumpy level) above the beds, ensuring fairly equal flows to each bed.
I do like the idea of winter circulation and aeration, so I might try to incorporate it somehow. I'll make an appointment and call in some time.

Posted By Colin Roberts on Monday 6th February 2012 @ 12:24:56


Good work Colin. Having the outlets level relative to each other is very important....unless you use a valve on each one to regulate the flow, but the use of valves costs more and needs a lot of fine tuning.

Posted By Murray on Monday 6th February 2012 @ 12:24:56


Hi Murray. My system is one of your chop2 successes.
Interested people northside of brisbane are welcome to organise an inspection- through you- if you like.

Posted By Adam on Monday 6th February 2012 @ 07:47:18


Thanks Adam. I must drop over one day soon and get some photos.

Posted By Murray on Monday 6th February 2012 @ 07:47:18


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