Backyard Aquaponics
A place to discuss aquaponics

I think it is about 30% more (400 vs 300m^/m^3 according to W. Lennard), but at 300% the cost, is it really worth it? I mix in smaller blue metal with my gravel, so probably have higher SSA than scoria anyway, at a fraction of the cost.

Simple answer is, no its not worth it, because surface area is important for bio filters not for GBs.

Arnt growbeds acting as bio filters in aquaponics?

Yes they are but its a minor function.

In terms of their bio filtration capacity GBs are WAY over sized.

GBs major function is to store solids while they are broken down and all the nutrients released. That is why they have to be so big.

Thanks for the clarification Stuart. Makes more sense.

Yes thanks for that maybe I will try gravel for the next system.

Ok but it wouldn't hurt to have the extra surface area scoria provides, correct?

And the scoria would be 300kg lighter than gravel in my system which is not insignificant?

I just checked and I can get Nepean River Pebbles delivered for $390 for 3.5 tonne

Of course I appreciate the saving - but at the end of the day I do not want to compromise on the function of the growbeds.

Thoughts?

No, it wont hurt, except the hip pocket... and maybe your fingers when planting seedlings!

Yes, 300kg is significant, but the extra cost is even more so, IMO. My GBs have no trouble holding gravel, both the thick walled, and the thinner less expensive ones, so it might only be an issue with weak walled/bottomed GBs or supports.

Ok so what do you think - do my grow beds have enough support to handle the river gravel/pebbles?

Growbeds 3 & 4 are sitting on the IBC cages cut vertically rather than horizontally - then placed on top of the IBC cages supporting the sump tanks.



Growbeds 1 & 2 are sitting on a support frame I built out of galvanized fencing which is cemented into the ground on one end and supported by a plastic pallet on the other end(see photo 1)



But before I put the grow beds on top I added vertical galvanised steel supports roughly halfway down (Also cemented in) AND put in place a few bricks I had lying around. The bricks have been packed with clay from burying the sump tanks. Growbeds 1 & 2 each have four bricks underneath them.


The view underneath GB 1 looking toward sump tanks:

oh geezus, you have been arounf long enough to know there is nothing wrong with scoria and if you get sore fingers..... you are using it wrong.... dont blame the scoria.

Just a thought you keep on switching between T and m3. Down here I can buy scoria by the tonne which is great because its weighs less. About 0.75t/m3.

On the other hand blue stone is about 1.5t per m3 (from memory).

Yes I calculated to fill my GBs I would need 2.75tonne scoria or 3.5tonne river pebbles

how do you guys even work out what you need using tonne??

in melbourne we use M3 at all times.

makes life easier to use volume measurements when you want to measure volume, rather than using weight.... :wacko:

hmm, IBCs out in the sun... do you know their age and history?

They will be fine for a number of years if they haven't had much sun/UV exposure, but I would be a bit concerned about the IBCs going brittle over time when loaded up. Best to paint or cover them to protect them from UV and prevent that happening if you want to keep the system going in the long term.

How well do the frames support the bases of the IBCs, ie no bent bars etc? I'd say they will probably be fine, but another option worth looking at is what I did with my first system- a mix of expanded clay and gravel, keeps the weight down without being too expensive.


Is that supporting pipe regular galvanised water pipe - ie quite thick walled & heavy?


Yav, yes I know its fine to work with, as is river gravel, but I know someone who complains about the roughness on their fingers

if you know people who complain, point out to them they are doing it wrong.

remind them to flood the bed well above media level so the media doesnt lock together, etc.