Backyard Aquaponics
A place to discuss aquaponics

I made most of my grow beds with plywood, 1 x 3 framing and pond liner.

I recomend the good heavy EPDM rubber pond liner. Your container is only going to be as good as the liner and with the cheaper stuff, you have to be so careful.

Yes, fold the corners, don't cut and try to seal.

As to if the plywood will hold up that amount of water, you will need sturdy timber framing to keep the sides of the tank from bulging out and eventually bursting apart. I've seen pictures of some big deep koi ponds made with wood and liner and the outside of the plywood had 2 by 4s edge in to the ply wood running horizontally to help keep the tank from bowing out. So long as you can keep the wood from rotting out in a wet environment and keep it from being eaten by bugs (remember that treated lumber must be kept from contaminating the system.)

As to how to figure out what size liner you need
Depth times two, plus length, plus a few feet for fudge = total length of liner needed
Depth times two, plus width, plus a few feet for fudge = total width of liner needed
so by this formula you need
(1.2m x 2) + 2.4m + 1m= 5.8m Long
(1.2m x 2) + 1.2m + 1m= 4.6m Wide

What I have found about buying liner here in the states (I like the firestone pondguard liner as it is really tough yet flexible.) They sell it in increment widths that probably correspond to the manufacture method. The narrow roll is 5.5 feet wide, next width up is usually 10 foot wide then 15 foot wide, etc. I can build nice inexpensive grow beds so long as they are only about 3' wide by a foot deep, any length goes. This doesn't work as well for the tanks of course. I've been able to get away with very little extra liner when building grow beds but when building a bigger/deeper tank, you need the extra liner since it is much harder to get it perfectly lined up and attached.

My big tank is in ground with some wood framing around the top edge above ground. I was lucky to find a really good deal on the pond liner for that tank though.

Good luck!!!!

that great thank you ,
1 ? though you have seem to have got a differnt total than rupe did ?
did he forget to add somthing ?
that lining makes my idea almost to expencive
it might be worth getting 5 of the green 500lt bins from (B)
again thanks for all the info ..

Fishlips TCL is right... figured the width correctly...

But forgot to add the two end uprights into my calc for length... and just rounded it....

Thank goodness someone checked, thanks TCL

I have Marron living with mussels quite happily, so can't see why yabbies wouldn't be the same, we have a mussel thread some where here, but to recap, Mussels need a host fish to breed, so problem is finding a fish that can live with yabbies and vice versa, as yabbies eat just about anything this will be hard, I found a small native perch lives happily with Marron and Mussels

+1
Folding reduces likely leaks, my tank is 1.2 x 1.2m by 0.8m deep and I am not sure I would be comfortable making one deeper, awkward to make the folds.

Folds like a hospital bed (reminds me of a girl I knew)
then put a rock/brick on the fold to educate it!

Large tanks of any sort will be costly unless you have a free sources of large bins/barrels/or IBC that are safe for use. That said, keep your eyes open for large chunks of liner that might have been cut for a specific job and then the job canceled. I think that is how I got my large tank liner at about 60 cents a square foot. If you can work out a design with the width perhaps on a meter and the depth just over a meter then put it in place very very carefully, you might not need as much extra for fudge but it is tricky to say.