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.


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 you can study if you watch and play the accompanying animation.

See Animation HERE

With CHOP2 you will notice that 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 Mark2?

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 Mark2 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 Mark2 is that should they decide to change their system from a gravel based media to floating raft, CHOP Mark2 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 Mark2.
People always vote with their feet. They know when they’re onto a good thing.

The next generation of CHOP.   CHOP Mark2

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

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5 thoughts on “Aquaponics CHOP Mark 2 Operating System.

  1. Thanks so much for all the information on your site! I am looking at setting up my first aquaponics system and would like to set-up a CHOP 2-type system.

    I have done alot of research and know how to size the fish tank and growbeds but have not seen any guidelines for sizing the sump tank. Could you advise me on this?

    Also, I live in an area with a definite winter weather situation so am looking to set the system up in my basement which is not heated. I am looking into a solar water heating system for the house and thought I would tap off that to provide a heat source for the aquaponics system. I was thinking of running a coil of Pex pipe through either/or/all of the fish tank, sump tank, and/or growbeds. Any thoughts on what would be the most efficient and beneficial?

    Thanks again, I am very excited about this project and owe much to you and your website for information and inspiration!!!

    • Hi Carl, The sump should be big enough to hold all the water from all the grow beds should they all drain into it at the same time. The volume of water in the grow bed is about one third of the volume of the gravel media. So, that will give you a guide as to how big it should be.
      Winter heating of water is a tough one. It is usually easier to heat the air to keep things warm than attempting to heat the water. The temp of the water will follow the air temp. As for taking water off your solar system, I guess you will not know how that goes until you give it a try, but I suspect it might rob hot water for your house use and not do such a good job of heating your fish system.
      I hope this is helpful to you.

  2. Hi Murray,
    I have recently changed to the chop mk 2 system, from 3 pumps (pumping to the growing beds, the solar heater ( and to the bio filter. I now have one 4800L pump pumping to two 300mm deep IBC tote growing beds (with toilet flush valves and bottles), the solar heater ,the bio filter and then to the fish tank (650L), so the fish (tilapia) only get clean water from the bio filter. I also have a cystern valve to automatically top up the sump when the level drops too low as well as a battery back up which switches over automatically and lasts for up to 12 hours. I will be uploading a video of my system soon on Youtube and will post the link.
    Thank you for a very informative Blog.
    Regards, Malcolm Meredith.

  3. What do the fish eat? I did not want to have a GMO fish farm, if you get my drift. We are curious as to how to have the cycle replenish itself so it could work year round as its own ecosystem. We did not want to feed the fish “unnatural” food. Thanks. IJ

    • Hi Irene,
      It is possible to feed the fish on natural food. Depends on what species of fish you decide to or can keep in your area as to how hard that will be. There is available organic certified fish foods in the USA so it is possible to raise your fish on a good diet.