Saturday, January 29, 2011

New SLO design, Video tour

Hi there

Long time no blog..
Today I put up another fishtank and built a pretty cool Solids-removal system for it.

The solids removal problem:
In aquaculture systems, solids need to be removed.  Why?  Well how you you like to swim in your own poop all day?  Seriously, the fishpoop solids can start to rot and create ammonia and all sort of nasty things we don't want.  Plus its nice to have a clean tank to show to visitors..

How is it normally done in AP systems?
In AquaPonics, there are two main methods to remove solids.  
Pump-in-Fishtank (PIFT): 
The pump is located on the bottom of the fishtank.  The pump picks up the solids from the bottom of the tank, and typically the solids are dumped in the growbed, where earthworms will take care of it..  Problem is that the solids are picked up OK, but only around the pump.  The opposite corner of the fishtank will remain poop-filled, and you will need to manually siphon it out, or maybe grab a net.

Solids-Lifting Overflow (SLO):  
 The fishtank has a pipe along its bottom with slits cut into it.  The pipe elbows up the side of the tank and from there heads out to the sump.  Sounds good, and works sort-of OK.  Problem is that again, the bottom pipe does not reach everywhere, and again you have some poop sitting in a corner.  A second problem is the size of the cuts in the SLO.  If you make them big enough to always pass all the solids, then, if you have smallfry, you run a real risk of getting some smallfry sucked in.  If you make the cuts small enough to keep smallfry from getting sucked in, then the cuts are likely to get clogged by poop and debris.  Not good.

So what is my idea?
I noticed that in indoor aquariums, the Under-gravel filters work wonders in collecting fishpoop.  In a typical aquarium, the poop sort-of collects under the filter plate until you eventually get around to cleaning it.  These filters work by creating a negative pressure area under the filter plate (which itself is covered by gravel).  Fishpoop gets sucked down through the gravel, through slits in the filter plate, into the cavity below the filter plate.  The reason it works so well, is that the filter plate and gravel diffuses the negative pressure, so there is suction all over the bottom of the fishtank, as opposed to one or two areas, as in the typical AP setup.  The other cool thing is that smallfry do not make a habit of swimming down deep into the gravel, So you have a system that can pick up all solids without any risk to the smallfry

My idea is to create an under-gravel filter that collects solids in the same way, but the solids are not collected and stored, but removed via SLO.  We create a filter plate with a negative-pressure area under the plate (solids collection cavity), and have gravel above the plate.  Solids are removed by a SLO mounted inside the collection cavity.

This is how I did it:

Solids-lifting overflow pipe assembly:
SLO pipe assembly
The pipe assembly features a split design that helps to spread out the suction beneath the filter plate

SLO Pipe Assembly showing cuts
Some cuts in the pipes allow the solids that are collected under the plate to be removed..

Filter Plate

Filter plate with cuts.  Cutting a perfect circle is not very easy.. 

Filter plate strapped to pipe assembly

SLO + undergravel filter mounted inside Fishtank
Completed Fishtank.   

Notice the dirty water, because of the gravel I added to the tank

Video Tour:
I finally made a video.  Enjoy!


  1. Hey there, I know it's been a long time since you posted this, I'm no expert in aquaponics but this system really makes sense. Good job!

  2. 5 years later.. how's it holding up? Any changes to the design since you posted this? Most importantly, can you provide details on the filter plate? What material is it made of, where did you get it, how did you cut it to shape, what size are those cuts, and anything else you can add for someone that's never seen nor done this before (i.e. the SLO and filter plate) Finally, can you explain why this is better than a simple standpipe drain with a casing for solids lifting? Thanks!

  3. Hi Noteguy..
    Yes the blog has been a bit stationary!
    The system as seen here, is actionally not in existence any more.. I had to move, and the system had to be broken up. What a job! - I still have the crucial bits (including a few fish) with me, and good news is we are now moving to a nice Smallholding where I will have space for AP to my heart's content! Watch this space!

    I made the filter plate out of a piece of nylon sheet, around 5mm thickness (I had it lying around). The slots were cut with an angle-grinder, so they are around 3-4mm in thickness. The reason I thought this SLO was better, was because solids are getting collected across the entire bottom of the tank, not just from the area where the pipes are located. The suction from the standpipe was as-it-were diffused by the gravel layer. It worked very well. The gravel provides additional surface area for bacteria as well, and i think it also provides an environment that looks a bit more natural, (to me, at least).

    Is it a must for a fish tank? - Not at all. It is a lot of effort to make this, without measurable benefit. I will certainly not bother to do this in a big fishtank. The fish are swimming around, swooshing the solids at the bottom anyway, so all of the solids do get picked up by a standard SLO anyway..

    I will be putting together a new, hosted blog, and will make a release here about it..