Backyard Aquaponics
A place to discuss aquaponics

Hi all,

About a month ago I was fortunate to do some work for the man who started Duraplast, a water-tank manufacturer up here in the Northern Rivers.

I had a yack with him about AP as it turns out that he used to do hydroponics many years ago and I thought he would be a good source of info re what to grow up here.

When considering my systems I have always considered flood and drain systems with the water flowing back from the drain beds to the fish tank via gravity. While talking to this guy about how I wanted to develop my systems I mentioned that I was thinking about either Concrete tanks or plastic tanks dug into the ground for the fish. He told me a couple of things and I was wondering if anyone could confirm or deny them for me.

Firstly he told me that I should never have concrete tanks as the concrete will kill the fish. He said that there are chemicals that leach out of the concrete that are toxic to the fish. Has anyone any knowledge about that, or experienced that themselves? Has anyone got concrete tanks for their fish?

Secondly, he mentioned that, if I go with plastic tanks then I have to be very careful how I bury them. He said that the tanks are designed for tension, not compression. eg, when full of water there is tension caused by the water pushing out from inside. If I bury the tanks there is now compression pressing on the outside by the soil etc. This compression will make the tanks buckle and possibly collapse. Has anyone experienced this? Has anyone got tanks that they have dug into the ground? If yes, how do you prevent the compression on the tank?

Thanks

Simon

Simon, C1 is your man for the concrete answer.

I have a 3/4 buried IBC..........i find that the water pressue keeps the walls straight, however the top bit that doesn't have much water "head height" does bow in a little. but then again the IBC is very thin HDPE

Simon,

the monster tank is a galvanised steel tank with 2.3m3 of 20/25 concrete in it to repair the rusted out floor. The concrete has reo bar as reinforcement also. The concrete rises up the sides of the tank to a height of about 80cm. The concrete was allowed to cure for a few days then the sides were coated with a bitumen seal. The floor of the tank is unsealed. The bitumen seal was allowed to cure for 2 weeks.

I have had 250 fish in this tank for 6 months now. Not dead yet

(did I get all the numbers right C1?)

I think he is right on both counts Simon. Plastic tanks will normally state in their wrranty terms etc that they are not to be buried. Regarding the concrete - probably wise to coat it with some sort of pond fish safe waterproofer or line it.

Simon, have a look here
http://backyardaquaponics.com/forum/vie ... 5466#15466

ive never seen those! you're hard core IV!

and here
http://backyardaquaponics.com/forum/vie ... 7418#17418

Geez that is scary!

We buried a plastic tank at school for our fish and it bowed inwards something awful! had to dig out all around it and clad the outside with corrugated sheeting, then fill in again behind the sheets - now all is well

Simon, the main problem is with fresh concrete. As concrete is a mixture of cement, lime, crushed stone, sand and water the ingredients are fairly harmless. The main problem is that the fresh concrete releases lime back into the environment and can change the ph balance of the soil and water it comes in contact with. As to harmful chemicals, this can be a local problem due to the extra additives that are added to the mix to retard or increase the rate of cure. If you plan on making your pour at a period of time when the temp will not drop below freezing, and will not rise above 85 degrees fahrenheit you can tell the batch plant that you do not want any additives put into the mix, as you need a finished product that will be chemically inert.

The recommendation to allow the concrete to cure for at least a week or two is important. Concrete, as it cures, produces heat and releases minerals and chemicals back into the atmosphere. Once you have allowed the concrete to cure, coating it is a very good recommendation as concrete is a pourous material and will wick water through itself. Another reason to coat the concrete is that you might have leaks through minute cracks between sections or that might develop later.

If you check with commercial hatcheries you will find that many of them use concrete raceways to spawn and raise thier fry and fingerlings. Here, where I live, both the state and private hatcheries use them for everything from catfish to trout.

Kevin

Good words Kevin, normal cure time for GP concrete is 28 days @ 20c.
I have said it before but find most free lime, salts etc accumulate on the outside of structures. It seems to be a need for drying conditions to grow crystals of contaminants.
The push of pressure is to the outside and as such have never seen a build up of freelime or other on the inside of a tank. Been in over 300
big tanks. Heaps of signs on the outside.
Lots of dead possums cats rats etc.
C1

This is what I love!

A forum where you ask a simple question and you get great, informative and useful answers.

Thanks heaps all.

Simon

Everone tries to help Simon....

Guess you could say this is the real Aquaponics HQ centre

P.A.F.E ?

Simon, the only experience had by forumers in burying plastic tanks is with square or rectangular shaped ones.

I have had my 400l rectangle one in the ground for 6 months now and it has bowed inward slightly, this one has been through a few incidents, like water flooding underneath and popping it, but it has retained its shape reasonably well.

Round plastic tanks may be different as the inward pressure would be spread more evenly.

The sides could be strengthened with some gal sheeting so that the dirt doesn't collapse into the sides.

What sized tanks are you looking at burying