Backyard Aquaponics
A place to discuss aquaponics

Does anyone know if a concrete septic tank (new), buried halfway in the ground, would make a good fish tank?

Is the top open and accessible? Can we have a picture? A few of our members do have concrete tanks, and I believe that they needed to seal them. One member had trouble with the concrete really pulling pH up (I think) and that would be my main concern. If you use a good sealer, the concrete shouldn't be a problem. My bigger question would be the shape of the tank, and whether you could get to the fish.

Hi DRG, wlecome to the forum.....

Ditto on what Janet said.... some concrete tanks can be slightly porous, hence the need to seal.... and tend to drag pH....

But ... yep some are using them....

C1 would be the man to ask.

you're probably going to have more PH issues with a brand spanker rather than a 12+ month old.

depending on your stocking density and feed regime this may be a source of buffering for you!

check with creative1 and do your own little test. fill her with water and measure PH over a few weeks

dgr- is it a 4 footer?
If so I think the porousity might be an issue.
PM me if you feel the need!

Wouldn't it be pain to get the fish out through the dinky little inspection hole?
(mine's about 1800mm diameter but lid is only around 600mm)

DRG... I note that elsewhere you say your tap water pH is 8.4

Think in that case that a new concrete tank will cause you problems not only with pH, but also when you try to cycle up....

The tank is 4 foot in diameter and 5 feet deep with no lid. We would be buying it new. And yes, it is the pH that worries me. We live close to a lake and river with high salt content, so all the water around here is pH 8.4 out of the tap. But in my inside aquarium the high KH of the water keeps the pH very constant. If we seal the tank would that solve the pH problem? If so, what product do you use to seal? Our other option would be to put a liner in it. Thanks so much for the feedback!

Do you have any chance of filling it and letting it cure? Remember all commercial raceways are made of concrete so this is not something new. Another thing that you may not be aware of, that is a bonus on your side, is the fact that concrete absorbs CO2 directly from the water.

Wonder how long it would take to cure? a year? Can you keep a husband from putting fish in a tank for a year???

I may have him convinced that a 300 gal rubbermaid tank will be big enough. Does anyone know of any issues with the rubbermaid tanks? like with pH?

Thanks again!!!

Nah, 21 days cure, and it is probably from stock anyway.
Get it going water helps to cure concrete.
some septic tanks (other than commerxial) are pretty porous.
So I figure you would have to line it or what will you do with the base.
Unless you know a fare bit about control jointing or some kind of combi flex
you will have trouble sealing the base. IMHO only!
C1

Those rubbermaid feed tanks are great for AP. A number of people are using them. Wish I were!

As a general rule, APers need to be a bit wary of black plastic, as it is often recycled, and there is no way to tell if it's been exposed to something that will leach nasties into the water. I haven't researched them, but I assume that since the RM tanks are for stock animals, they're safe to drink from, and therefore safe for AP.

Rubbermaid tanks are awesome. I use 3 50gal rubbermaids for the growbeds, and a 150gal rubbermaid for the fish tank. They are very inert and very sturdy. No problems with the sides bowing out from the heavy gravel or anything.

Here's the spec sheet for Rubbermaid plastics.

http://www.rcpworksmarter.com/rcp/products/pdf/chem.pdf

The stock tanks are made of "structural foam". I never have been sure which of their plastics that is. I wasn't too worried since any of their plastics are rated Good or Excellent for anything I was likely to put in the tanks.

Rubbermaid tanks are great! I can climb on the edges of mine and the sides do not bend out. I have two 300 gallon tanks and a 100 gallon. They cost about .64 cents per gallon when not on sale.

If you do use a septic tank then make sure it cures well before you seal it and then paint it with potable water paint, or put a pond liner in it.