Backyard Aquaponics
A place to discuss aquaponics

Well I don't know if this is so new, but have a look anyway..
Would love to hear some feedback on this idea.
I constructed one today, and I am pretty happy with it..

I copied this from my blog:

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:





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

Looks Like a great design and you have put a lot into it, i cant see why it wont work well, i'd just watch how much gravel you use as the solids may build up in the gravel and affect water quality.

But everything here is a big experiment, keep us posted on water quality and how the Solids removal works, if the gravel or plate become blocked a little it may cause the tank to over flow also, so id keep an eye on that

In a lightly stocked Ap system I think that this would be fine but most people keep fish at much higher densities than those that you see in aquaria.

I think that most of us would be better served by just copying methods from aquaculture. ie no pumps in the fish tank and use the rotational velocity of the water in the tank to concencrate the solids in the center where they can be removed via a center drain.

From what I have seen at aquaculture joints, they still have a real problem on their hands.
I have one round tank where I am using the swirl motion to collect solids, but there remains a problem at the point of collection. The holes are either too small (gets clogged up) or too big (smallfry get sucked in). If you remove the smallfry into separate tanks (as they do in AC) then in those smallfry tanks you again have the same problem. From what I have seen, in AC smallfry setups they just live with the muck, and manually siphon it out every now and then.

I see no reason for the gravel to get clogged up, because it is really big gravel - 3/4", same as in the growbed. And I only have an inch or so of the gravel. The slots in the plate is also rather big. Somehow the fish do not tend to swim that deep into the gravel, and thus I should theoretically not run any risk.

I am going to use this tank as my brooding house. Will add a few females and one male. Shucks. I hope the eggs do not end up getting sucked down into the gravel.. Did not think of that one..

IF the gravel or the plate gets clogged, I may have an overflow problem indeed. Should maybe consider adding an additional overflow at the top for that eventuality..

Hi bassmonster,
Any update on your SLO? I'm designing another system for my hoop house and would like to hear how it's working.

Mikey

Hi Mikey

I actually emptied that tank over the weekend to have a look at it.
The gravel idea works very well in my opinion. It never became clogged. The gravel stones did get some brown and black stuff on them, but this is expected. There was no accumulated solids to be seen. As an added bonus, the male tilapia seem to love it because it is more natural - the gravel provides them with the opportunity to make a real nest. They tend to dig around in the gravel to make a hole.

I would next time prefer more gravel, because the males tend to dig too deep and then they expose the filter plate (which is not that bad, but not ideal). I used maybe 1-2 inches of gravel. Would prefer 4-5 inches next time..

It would be interesting to do this sort of SLO on an IBC tank. It would be a bitch to create the filter plate though..

regards

Theres a design for an SLO which has large shallow plate where it leaves the tank, Water come up from floor of tank, using 45 deg and uniseal, into floor of plate, then exits accross other side down through 90 and out.
A coarse screen here stops escapes and if it sucks from the centre of the tank works very well at removing waste and stopping fish leaving. They can access the plate but jump out or go back down the SLO. Water level here is ~ 22mm (3/4) deep
Screen is large and at surface level so easy to clean, cant block up as if it does water level rises, and goes over the top, which exposes much larger area of screen.
Credit for this goes to Paul from another website, I drempt up the screen idea I think.
Another benefit is the whole unit can easily be removed and replaced.

Interesting idea.....

Have to keep it well out of the sun light or it will become just a big green algae blob on the top of your tank.

Interesting..
What do you have at the bottom?
Does it just end in the middle?

How then does it remove solids from the corners?

Yes the tank is covered with a coreflute lid, it does get a bit of algae but only the same as the rest of the tank
The bottom end is just cut at 45 deg, the important part is to have the suction in the middle and get a bit of motion going with incoming water. It wants to happen by itself so doesnt take much. Depending which hemisphere as to which way the swirl will want to happen. Just like the toilets!

Even without swirl the solids just move towards the centre with fish movement.
I have used, when fish are very small, a 12 Watt open impeller "wave maker" pump to get this swirl motion happening but it sucks feed up before fish get to it so its really too effective and needs to be turned on for just a few hours a day.
Just pointing incoming water in the right direction gets a circular flow happening.
I have 2400 lph going through each IBC.

Coriolis effect, but unfortunately it's an old wives tale when it comes to toilets, hand basins, AP tanks etc.. Coriolis effect plays pretty much no part in which way the water swirls.

Your probably right, but we have a large volume of water sitting still, possibly it can be seen??
US toilets often have much more water volume than Aussie equivalents, ours cant swirl even if there was a coriolis effect.
In either case its not very hard to get enough movement to make the SLO work

+1 Earthbound is right.

I wonder why that is?
Could this be the first scientific proof that americans are full of sh*t?
Sorry, I could not help myself there! - no offense intended.

You know in my system I've noticed that the #1 thing that keeps the tank clean are the fish themselves. All that movement keeps the solids from settling. In my opinion it's not mentioned enough. Instead there is all this talk about swirl action of the tank and creating some special solids lifting device. I even noticed if I take out the SLO and let it overflow normally the fish still kick up all the solids and the tank stays clean. (I still like the SLO though, water comes in from the top and out from the bottom, seems better to me)