DIY Solids Filter

DIY solids filter

Many people have asked me how we built our “Fresh Flow Filter”. While that diy filter is very effective in the 4000 litre system it does require some plastic welding, which most people do not have access to.  They also asked for a bit more of an explanation of how the filter actually works.  So here is an explanation of how the fish solids filter works along with a drawing (plans if you like) of how to build a DIY solids filter at home in a 200 litre blue drum

DIY Solids Filter

The Fresh Flow filter is basically what is called a radial flow filter, as that description may not mean much to anyone here is a bit of an explanation using the attached plans below for a DIY solids filter you can make at home.  This filter has been copied by hundreds of backyard farmers with many of them adding their own twist.

The orange pipe inlet

The filter is generally set up at the same height as the fish tank,  the fish waste water flows from the fish tank to the filter by gravity through the orange pipe.  That pipe can be used to control the water level in the fish tank.

The outer ring or pipe

The pipe or outer ring around the orange (inlet or effluent) pipe can be 150mm pipe, a 70cent plastic bucket upside down over the inlet pipe.  This forces the water flow to the bottom of the filter tank where the water changes direction to flow towards the green outlet pipe.  When this happens, the heavier particles (the wasted feed and fish poop) falls out of suspension to the bottom of the drum.

The green outlet pipe

The outlet pipe generally runs to your biofilter or the next level of finer filtration (not often required).  The level is set  below the lip of the blue drum.  You will notice that outlet has a reducing socket or flange on the top of it.  This is to increase the surface area of the outlet but is not entirely needed.

The gold dump pipe

This is pretty simple some form of dump valve on the bottom of the tank. You can either make up a conical bottom in the drum to concentrate the solid wastes near the dump valve, however not entirely needed but handy to have.  You can use a simple elbow facing down in the bottom of the tank with what is called a “puddle flange”.

The diagram of the DIY filter below will help to clarify some of the fittings and set out of the filter.  I would use Uniseals to put the pipes through the wall of the tank.  The top angle to support the outer ring can be anything that will hold the pipe or bucket in place and it does not need to be in the centre if that makes life easier for assembly, though it works better in the centre.

DIY solids filter

I hope you have found this to be useful and if you have the time, please send in photos of your copies and variations of our DIY Solids Filter

Regards
Paul

Many people have asked me how we built our “Fresh Flow Filter”. While that diy filter is very effective in the 4000 litre system it does require some plastic welding, which most people do not have access to.  They also asked for a bit more of an explanation of how the filter actually works.  So here is an explanation of how the fish solids filter works along with a drawing (plans if you like) of how to build a DIY solids filter at home in a 200 litre blue drum

DIY Solids Filter

The Fresh Flow filter is basically what is called a radial flow filter, as that description may not mean much to anyone here is a bit of an explanation using the attached plans below for a DIY solids filter you can make at home.  This filter has been copied by hundreds of backyard farmers with many of them adding their own twist.

The orange pipe inlet

The filter is generally set up at the same height as the fish tank,  the fish waste water flows from the fish tank to the filter by gravity through the orange pipe.  That pipe can be used to control the water level in the fish tank.

The outer ring or pipe

The pipe or outer ring around the orange (inlet or effluent) pipe can be 150mm pipe, a 70cent plastic bucket upside down over the inlet pipe.  This forces the water flow to the bottom of the filter tank where the water changes direction to flow towards the green outlet pipe.  When this happens, the heavier particles (the wasted feed and fish poop) falls out of suspension to the bottom of the drum.

The green outlet pipe

The outlet pipe generally runs to your biofilter or the next level of finer filtration (not often required).  The level is set  below the lip of the blue drum.  You will notice that outlet has a reducing socket or flange on the top of it.  This is to increase the surface area of the outlet but is not entirely needed.

The gold dump pipe

This is pretty simple some form of dump valve on the bottom of the tank. You can either make up a conical bottom in the drum to concentrate the solid wastes near the dump valve, however not entirely needed but handy to have.  You can use a simple elbow facing down in the bottom of the tank with what is called a “puddle flange”.

The diagram of the DIY filter below will help to clarify some of the fittings and set out of the filter.  I would use Uniseals to put the pipes through the wall of the tank.  The top angle to support the outer ring can be anything that will hold the pipe or bucket in place and it does not need to be in the centre if that makes life easier for assembly, though it works better in the centre.

DIY solids filter

I hope you have found this to be useful and if you have the time, please send in photos of your copies and variations of our DIY Solids Filter

Regards
Paul

About the author

Paul Van der Werf

Paul is the Operations Manager for a 4400m2 integrated aquaculture pilot project in the United Arab Emirates desert he designed and built. This is a commercial aquaponics pilot to evaluate integrated farming in arid climates.

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43 Comments on “DIY Solids Filter

  1. shaunmavronicolas

    Hi Paul, there seems to be a little more magic happening with the version you have on YouTube, the black second baffle… are you able to share any of these details? Also, does the second baffle go all the way to the bottom of the barrel, with just a small gap or is it a similar length to the first baffle?

    If you can’t share any other details I understand, clearly you’ve spent a lot of time getting this to work so well, from what I saw in the video.

    Many thanks,
    Shaun.

    1. Hi Shaun,

      If you take a look at the School Aquaponics Video 3 of 3 the construction photos and skip forward to 1:00 the following photos show how it was built.

      That will give you a much better idea.

      Regards
      Paul

      1. shaunmavronicolas

        Many thanks for pointers Paul. I’m busy building a DIY drum filter for our backyard setup and stumbled across what you had made and for simplicity, clearly it is a winner. It looks like it works so well that I am questioning my drum filter solution. I have very limited space and my drum filter can fit into a 2ftx1ft foot print, but it is a lot more complex to build and make reliable. You’ve a wonderful library of very helpful information, thank you for sharing this all.

        Shaun.

        1. You are welcome Shaun and thanks for the feedback.

          Regards
          Paul

  2. shaunmavronicolas

    Hi Paul, I just clicked on the image above and it took me to another post with a 20L pain bucket, is this the second rim that is visible in the YouTube video?

    Many thanks.

    1. Hi again Shaun,

      That particular DIY filter is a swirl filter. A slightly different type of filter for the do it yourself enthusiast. They work well but not quite as good as the radial flow filter.

      Regards
      Paul

  3. Noddy65

    Hi Paul
    Im thinking of doing something similar for a multi tank fish room (50 tanks)….I was going to use a swirl filter but this seems to be better….can the water from the fish tank enter through the open top of the blue barrel and then do a U turn to become the orange pipe in your drawing? Would it also be possible to use additional mechanical filtration (sponges, matting) between the pale green pipe in your drawing and the wall of the blue barrel or would this slow water flow down too much?
    My plan is to then have the water gravity feed into another blue tub filled with moving K1, then into a sump and then pumped back into the tanks.
    Ive got a 16,000 lph pump so will have to use 90 mm storm water pipe for most of the plumbing…can you see any major issues with this….

    Regards
    Mike

    1. Hi Mike,

      You can certainly have the water from the fish tank enter the top of the filter (replacing the orange inlet pipe) but you risk the water stirring up the bottom where the solids settle out. You can add sponge in the filter but this may be better off being in a separate tank, like your sump.

      Your flow plan looks good but the 90mm pipe may be a little too large but it will work.

      Regards
      Paul

      1. Frank De Block-Burij

        There is a very simple solution to an over the top inlet: just hang another, smaller bucket (with bottom) under the inlet, into which the water flows (splashes), the water then has to flow over the rim of this bucket. It will function as a first baffle to slow the water down and will also increase natural aeration of the water without any added energy.

  4. solarmon

    Hi Paul,

    I like the idea of the radial flow settler, since it seems simpler to construct compared to a swirl separator (no need for a cone).

    I’ve come across the follow commercial radial flow settler that seems to be what your DIY design is based on:

    http://www.w-m-t.com/Products/Radial_Flow_Settler.php

    which had a link to a technical description of how the radial flow settler works:

    http://www.w-m-t.com/library/pdf/Radial_Flow_Settler_Whitepaper.pdf

    In this document it actually talks about converting a swirl settler in to a radial flow settler.

    Is it correct to think that the ‘black baffle’ in your video represents the v-notched weir in the document? I assume this weir required to provide the ‘radial’ flow of water to the single outlet? Can this weir be replaced by an outlet pipe construction that circles where the weir would be? This pipe construction would have holes all around it to allow radial flow, similar to the v-notched weir.

    This leads on to my question of whether the container needs to be round for this to work? Can the container be square? This would make construction above outlet pipe construction easier – i.e. using just elbow joints.

    Is it correct the main attribute/benefit of this ‘radial’ flow settler is not that fact that it is radial, but the fact that it forces the solids (through gravity) to the bottom of the container. Thus, technically, the container does not need to be circular?

    Thanks in advance for your response and for the great blog.

    Cheers,

    SolarMon

    1. Hi SolarMon,

      Yes an outlet pipe would work well for the v-nothced weir. The idea of the v-notch is it alows the clean water to be taken from the surface more evenly than a straight edge because not all things will sit perfectly level. If it was a straight edge and there was a slight tilt in the floor, the water would tend to come up and over mainly the one side.

      Yes you can have any shape you like, though the radial flow filter should still have a conical bottom (though not entirely needed) to concentrate the solids at the waste outlet.

      Thank you for your question.

      Regards
      Paul

      1. solarmon

        Hi Paul,

        Thanks for your quick response.

        I was thinking of having slits at the top of the outlet ‘weir’ pipe – so I’m hoping this would act in the same/similar way as the v-notches.

        For the solids, I am thinking of have a cross shaped solids lifting pipe going to the solids outlet, with slits at the bottom of it – i.e. a SLO (Solids Lifting Over-flow). This should hopefully take most of the solids from the bottom of the container.

        I’m just trying to ,make the construction as easy as possible, without being too ineffective.

        Cheers,

        SolarMon

        1. You are welcome SolarMon.

          Slits will work well enough but be sure to make them fairly large as they will foul up and reduce water flow resulting in overflow.

          I will be putting up my solids filter in my little fish farm perhaps this week. It is a very simple and effective set up. In that I have a flat bottom drum which I put together an outlet which seems to work well directly out of the bottom. I like the idea of less fittings and simpler filters making them easier to clean.

          Regards
          Paul

  5. David

    Hi Paul,

    First of all, excellent job. I am looking at using 3 of these in a new fish room (120 tanks, around 15,000L).

    What would be the maximum flow rate through these filters before the heavy flow decreased the efficiency? Each filter would be taking around 50,000 L/hr.

    I was thinking of adding dual clean water outlets on either side of the drum to allow better flow escaping the drum, as well as using larger diameter pipes within the drum.

    Similar to Mike, most of my plumbing will be in a minimum of 90mm.

    Would placing micron socks inside a flange on the clean water outlets be feasible?

    Any suggestions are appreciated,

    Cheers,
    Dave

    1. Hi Dave,

      Thanks for the positive feedback.

      You will need to increase the outlet pipe size or double outlet as you suggested. I have 3200 litres running though my set up per hour with 40mm inlet and outlet, however approaching 4000 litres per hour the outlet needs to be increased to at least 50mm.

      I would avoid any additional media (socks) anywhere in the filter. You can use packed k1 after the radial flow to take out more solids. However I find a simple bag filter after your water pump and sump is very effective at getting the smaller micron out. Generally a 50 micron will do the job but good to have a 25 micron bag on hand. Cheap and effective.

      You are looking for a loading rate maximum of 200 LPM per m2 (5gpm per ft2) and a retention time in the filter vessel of 30 seconds. The loading can be as low as 120 LPM/M2 to adjust for the drum should you need to. The retention time can go up to 4 minutes but quicker is better.

      What that means is you look at the surface diameter of the drum you plan to use. Lets say it is one of ours with a diameter of 600mm. The area of it is 0.332 m2. I multiply the 200 lpm by the area 0.332 m2 and get a surface loading rate of 66.4 lpm for the surface area.

      Now I have to check the volume of the drum will provide the retention time of 30 secs.

      The drum is 200 litres but we only use 180 litres of it at operating height. We divide the 180 litre capacity of the drum by the flowrate per minute 66.4 which gives us about 2.7 minutes retention time in the drum.

      I am happy with this as it is within the range of 30 seconds to 4 minutes and works very well. However I have the capacity to push the water through the one I use much faster. In this case I could use a drum the same diameter and half the volume easily.

      Hope that helps.
      Regards
      Paul

  6. jimmy bryant

    i thought we want the fish poop for the plants

    1. Very true Jimmy.

      The fish solid wastes carry about 10% extra nitrogen and majority of the phosphorous (fish only take up about 5% of the phosphorous in feed the rest comes out their bums).

      So yes it makes perfect sense to use these solids wastes throughout your garden. If you are using floating rafts, then the filters will definitely come in handy and if you are using a media bed, the filters will help extend the life between cleaning out the grow bed (this is a good example here).

      Using solids filters does not mean you are wasting those great nutes, you can dilute them, make compost tea out of them and introduce them back into your system as you need them through foliar sprays or tonic solutions added to the water.

      Filters simply give you a great deal more control over what happens in your system and will permit you to carry more fish.

      Not to say solids filters are needed in every backyard situations, there are plenty of examples of small, lightly stocked media systems that work well enough. From my point of view, if you want to get more out of your aquaponic or integrated system in the backyard, filters are a very inexpensive and simple solution to help you achieve more productivity at home. At a commercial level, they are imperative.

      Regards
      Paul

  7. Cecil Baird

    Paul,

    The description says the green outlet pipe is lower than the orange inlet pipe, however, in the illustration with the flange attached it appears it’s higher. Does the added flange not count for the height or is the illustration off a little?

    Thanks,

    Cecil

    1. Hi Cecil,

      Good pick up. The green outlet is generally higher than the inlet. The illistration correctly shows how the outlets are.

      I will correct this now.

      Regards
      Paul

  8. Paul,

    Thanks for your quick response! I notice things like that because it doesn’t take much to confuse me! LOL

    What do you think of a gate valve in the inflow line to close, and then a complete drain of the drum to combine a removal of solids and then a water change by adding fresh water?

    1. Hi Cecil,

      I would like quite a few things on it. An inlet 3 way valve to completely bypass the filter for cleaning, a connical bottom to concentrate the solids, and a valve on the waste outlet that is left slightly open to create an undertow in the filter and leave no need to remember to drain off the solids (or a solinoid valve on timer). That would remove the solids from the water column immediately rather than letting it stew in the bottom.

      Regards
      Paul

  9. Simmo

    Hiya Paul,

    Thanks for this, and all the other cool stuff on your site. I found your page through Reddit, there is a sub-reddit dedicated to aquaponics and often people post links to your site. I’ve been tinkering with aquaponics for about 5 years now but still learning new stuff all the time.

    I knocked one of these up in 2 days from scratch, your diagrams and descriptions made my job very easy, so thanks!

    I use it in my system to collect all the uneaten food and solids from my Barramundi tank.

    These solids would eventually make their way to my growbeds, but I was constantly cleaning my pump out and the irrigation pipes, and my flow rates were suffering cause of all that gunk. My pump was working harder than it needed to as well…

    Now – I can simply dump this stuff off into a bucket and transfer it manually to the growbeds or dirt garden and my sump tank is crystal clear.

    Cheers!

    1. Hi Simmo,

      Thanks so much for the positive feedback.

      Glad you found the filter useful. Would love to see your version of it!

      Regards
      Paul

  10. John Baumer

    Hi Paul,
    Love your site. Thought I would share a skimmer idea for a radial separator. I believe that it is an old washer dump hose. http://s677.beta.photobucket.com/user/johnbaumer/media/Aquaponics/IMAG0625.jpg.html?sort=3&o=9
    I used a top entry 3/4 inch supply line that enters near the skimmer and makes a u turn to dump in the middle of the 6 gal bucket. I will post this soon.
    Keep up the great work!
    John

    1. Love it John. I hope others give it a go too. Looks like a champion idea.

      Thanks for the positive feedback. Always great to see other DIY ideas.

      Regards
      Paul

  11. John Baumer

    Thanks Paul,
    Added a few more pictures. Getting about 2 gallons per minute. Is that about right for a 200 gallon system? Is air injection in the bio essential?
    Thanks,
    John
    http://s677.beta.photobucket.com/user/johnbaumer/library/Aquaponics

    1. Thanks for more photos John. Love the cone on the bottom, what is it?

      You are looking for a maximum of 4 minute retention time in the filter. That will do for both bio and solids filters or they behave a little differently and become settling chambers, which is not a bad thing. The idea of the radial flow is to reduce the cost and foot print of the filter so generally you can have a much smaller drum in comparison to a settling type of filter with a 20 minute minumum retention time.

      Not sure how big your drum is but I will guess at 50 gal (200 odd litres?) If you are exchanging that 200 gals per hour though that drum you have a retention time in the filter of 15 minutes. Not a major drama. How it works is not as important as it working. If the filter is doing its job, leave it at that.

      Air injection is usually essential in any submerged type of filters, especially a moving bed type, even some trickle filters have air blown into them. If you are using a packed media type of filter (eg a growbed) then no, providing the flow rates are increased to keep the oxgyen up to it.

      Regards
      Paul

      1. John Baumer

        The cone is an old Christmas tree stand plus a flange from an air conditioner fan (sometimes it pays to keep JUNK). I have one in the bottom of the radial and believe I will add another to the swirl/surge tank. Flow rates are; 1.25 gal/min. skimmer on radial and 1.25 gal/min. drain on radial equals 20 minutes retention on 50 gal. 1.25 gal/min. bio filter equals 40 minutes retention on 50 gal. The bio filter is fed from the bottom by the drain on the radial separator. 2.5 gal/min. on the system equals 80 minutes to put the 200 gallons from the fish tank through the filters. One note, I had a difficult time getting the siphon stopped on the grow bed until I put a tee in my return line to the fish tank. This allowed the flow to continue without continuing to pull more water from the grow bed.

  12. Tim Jones

    Excellent job! As I can see from reading here, creating a swirl seems to be the thing to aim for. Does this mean the fish tank should be round also?

    1. Hi Tim,

      A round fish tank certainly helps get the solids out of the fish tank and into the filter. However, they can be any shape.

      Regards
      Paul

  13. Richard

    I have 65mm pipe coming out of my 2000L fish tank to the growbeds. Is this too big for a 200L blue barrel filter
    I really want to make of of these tomorrow as i found a blue barrel today. Rare as hens teeth around here

    1. Not at all. 65mm if that is what you have, it will work just fine. Be sure to not glue any of the pipes inside the drum. What I do is remove the vertical inlet in the radial flow and that increases the flow to flush the crud out of the line.

  14. Chris

    Hi Paul,
    This is just awesome information. I have a 300 gallon tank set up separate from my aquaponics system that is dedicated to growing out fingerlings. How would I keep them from being sucked into the pipe that goes to the solids filter? It seems like putting a screen or something over the pipe would defeat the purpose of getting the solids out. Thanks so much for the info you put out – I have learned so much from your website and gotten a lot of inspiration for different projects!
    Cheers,
    Chris

    1. Hi Chris,

      In one of my youtube vids I show what I put on the bottom of my pipes in the tanks. Bit hard to explain in words.

      Regards
      Paul

  15. tim

    do you put the pipe 40m under the water or half that thanks paul

    1. Hi Tim,

      Not sure which of the two pipes you are refering to. The middle one is set to the height you want the water in the fish tank (optional) the other sets the height in the drum so it does not overflow. Don’t glue any of the pipe work in the filter so you can adjust as needed.

      Regards
      Paul

      1. Hi Paul,

        Very impressive.

        Do you sell any radial flow filters ? Or know of anyone who does in Aus?

        Cheers

        Ross

        1. No not in Australia. We make them to order if required but will not be able to do so for some time.

          Regards
          Paul

  16. tim

    thanks paul i got the idea now….

  17. Fair enough. In that case I’ll have a go at making one based on your design.

    Just to confirm a RFF requires a

    - loading rate between 120 and 200 LPM per m2.
    - maximum retention between 30 seconds and 4 minutes.

    So for peak performance does that mean splitting the figures down the middle? ie: 160 LPM/M2 loading and a retention of 2.25 minutes?

    Thanks
    Ross

    1. Hi Ross,

      Yes you can choose which area yours will fit into. As long as both are within the ranges provided they will work very well.

      Regards
      Paul

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