Backyard Aquaponics
A place to discuss aquaponics

I'm having some fun in Sketchup and I'm starting to get a hang of the program.

I've just finished the main part of my grow bed design. It consists of a wooden frame with EPS foam on top. The EPS is covered with a 1cm thick layer of ferro cement and the sides of the GB are also made of 1 cm ferro cement.

The bottom is slightly angled to let the water flow into a gutter located in the center and running along the length of the GB.

The gutter is covered with a gutter guard to prevent the grow medium from washing into the gutter. A thin layer of very coarse gravel lets the water flow through the gutter guard. Finer gravel is used to top of the GB.

A little tank will be attached where the gutter exits and it will house the siphon that will empty the GB once it has been completely filled with water.

I have uploaded the Sketchup model to the download page.

Comments much appreciated!

Will you have access to the growbed from both sides? You will need that access to be able to reach to the middle of the bed.

I can't quite visualize how the little tank and autosiphon will be fitted to the growbed, but I'm glad you're thinking about it. That gutter should really help get good drainage from the whole bed. I'd consider coarser gravel for the bottom 30mm of the whole growbed to get even better drainage.

The only vague concern I have is whether roots might eventually clog the gutter guard. Think about skipping the gutter guard, and just using very coarse gravel in the entire gutter.

It looks good, You might find that a bed with such good drainage doesn't filter out solids too well, as the sloping bottom would probably channel all the solids down. But then depending on fow the water flows into it, it might do fine. I love the original idea though...

Yes, the GB will be accessible from both sides. I think 1.60 m wide is a perfect size for that, I've been trying how far I can reach when standing at the dining table and 80 cm is about how far is practical from each side.

I'm going to put the siphon inside rather than outside. Have a look at the attached picture, it is the GB cut in half, so you can see the location of the siphon.

Daniel, I'm not sure how I will be filling the GB yet, but I was thinking about adding a perforated hose along the long end on each side buried about 2 cm deep, so there will be enough substrate to catch the solids I guess.

Nice sketchups man. Those beds will use just under 600lts on the fill cycle if that helps. Other advice is out of my league. Can't wait to see it up and running Nico.

very nice, then. I think you'll be fine with the solids, too.

Be aware that siphons don't like sharp bends. (I'm having all sorts of trouble with a drain getting airlocks atm.

You'd be much better off using a nice flexible hose in a wide circle.

This is because the water will take the easiest route, so draw a circle about the bend and that's where it will go. Therefore air will be more difficult to push out of the corners, unless flow is very high. If you have a nice gradual bend, the water will be at an even force across the pipe, making the clearing of water easier. perhaps a tight bend in the PVC itself will work, but I wouldn't use fittings. Siphons are pesky irrational beings, so treat em nice, and give em every creature comfort.

I'm wondering if you'll need slightly stronger sides to the bed. Gravel is pretty damn heavy and 1cm thick cement over 3 metres wouldn;t be strong enough I don't think... C1 would be the one to answer that one though..

You might get away with 3 cm if you have reo-mesh or something in the middle, but even that is pushing it...

Forgive me if I'm wrong, but didn't he say he was using ferro-cement? Isn't that cement board? how does one add reo-mesh to this? also isn't board stronger than concrete?

ferro cement is chicken wire covered with sand/cement. It's supposed to be very strong. They build 1000L water containers measuring 1 x 1 x 1 m with sidewalls of only 1.5 cm thickness. So I guess a 30cm deep grow bed should be strong enough with 1cm sides.

Only one way to find out... Don't forget that you will have a lot more weight with grow medium. You will need to join the corners properly. That is were is will be the weakest....

you may find it less prone to crack if you make the corners rounded

(see i do listen C1)

Are you sure that they can make square (cube) tanks without burying them or adding some sort of reinforcement?

I can't seem to find any online.. only round tanks, which is the most logical and the strongest shape.

I'd be concerned about the square shape, the force exerted upon the corners is tremendous compared to the side walls. I'd frame it with steel or timber if I didn't want a flat tank after 10 minutes.