Backyard Aquaponics
A place to discuss aquaponics

Of the four things I listed above number 2 is the one I started on today.

I've had two of these gal tanks for about 6 years. Originally they were one tank but I cut it in half to make two fish tanks but then my plan changed.



These are the rolls of liner that I bought for the tanks and DWC.



This liner is the best I've found. When the Morwell river broke into the adjacent coal mine and the highway was closed because of fears it was going to collapse into the mine, this liner is the liner they used to line the canal they made to divert the river to keep it out of the mine. HDPE was rejected because of its shorter life span, lesser tensile strength and a number of other factors.

Needless to say it is seriously tough but best of all it can be cut and welded relatively easily.

First step is to prepare the base of the liner. Here I've welded two 3m pieces together.

Next step is to move the tank onto the base and I then trimmed the base into a circle from inside the tank.

After this I started hanging the sheets to form the walls of the liner.

How do you weld the liner?

That is one of the beauties of it. HDPE welding gear costs thousands. This stuff is welded with a gas torch.

I'll take some photos of the gear tomorrow.

Good to see the old get getting some love Stu.

Hey Stuart did you say what the liner was made from, sorry i missed it if you did.

Once I welded some builders plastic to make a pool cover, I clamped it together between some Ali SHS and run a oxy over the joint, it lasted about 3 years of abuse till one day the cat "jumped" on it and it broke (but not at the weld). It is sad to admit I was humored watching the cat walk on the cover over the pool water.

Actually I didn't say.

It is not plastic.

It is made from a non woven geotextile (ok so that is plastic) soaked in bitumen, about 1mm thick, with extra layers of bitumen on both sides about 1mm each making up an overall liner thickness of ~3mm.

HDPE has a life expectancy of ~20 years but I've been told this stuff should last 50+ years. In buildings it is garunteed to last 100 years or the life of the building whichever is longer.

Also repairing it is much simpler. It is very difficult to repair HDPE because the liner oxidises and that has to be scraped away before a patch is welded to cover a hole and it involves expensive equipment and good skill. With this stuff you just cut a patch and weld the patch on by melting the bitumen and pressing the two layers together.

Bitumen...

Umm... would that not leach some nastiest..?
..
.

Human safe.

Fish safe.

and the big one...

CRUSTACEAN SAFE.

The European Union has some of the toughest quality control and environmental regulations in the world. For example they banned the use of flexible PVC liners for water containment years ago. This stuff is approved for use for potable water storage in Europe and tests on fish and more importantly (because they are so sensitive) crustaceans have found that there are no adverse toxicities from using this liner.

Having said that modern scientific methods of investigating adverse effects are flawed due to the constraints placed upon the testers (budget and longevity of tests) but then testing regimes of all industrial materials operate under the same constraints. It is not possible to prove this material is safe but it is possible to say that there is not evidence to suggest it is unsafe and there is ample evidence to conclude that other materials are unsafe.

So far in my research there are three competing safe liner systems:

Polyethylene (HDPE, LDPE, LLDPE)
EPDM
Bituminous Liners

HDPE beats Bitumin on cost of purchase but loses on cost of installation particularly on small scale projects (1000m2 or less)

LDPE and LLDPE can beat bituminous liners on cost of purchase and installation particularly in small jobs ware there is no need to do any welding of liner pieces. As soon as you need to weld bituminous liners win.

EPDM loses on cost of purchase and is roughly equal on cost of installation but is not as durable.
PE is also not as durable and is not easily reparable.

I don't think bituminous liners are going to take off in the BYAP community because they are probably massive overkill for most people and the liner is very heavy. Also the welding gear costs about $500.

Finished the welding on the round tank liner today.



The key piece of welding gear is a gas torch.



The rest of the gear is a round nosed trial and a roller. This gas torch is a 45mm torch which is what is used for the detail work. A bigger 80mm gas torch is used for large seams.

cool

That is only the 45mm nozzle.


You should see the 80mm nozzle

wow - very kewl

Bother.

Started filling the new tank this morning. Should have checked the seams a bit better. Rather large leak which I think I can see from outside the tank so I don't know how I could have missed it when checking the seams from inside the tank.