Backyard Aquaponics
A place to discuss aquaponics

Someone named Lennard (or similar) wrote a spreadsheet for calculating the required size of growbeds and his values changed depending on which media you selected, but at the time of looking at his spreadsheet, I couldn't find anything he or anyone else had actually done to test these things. I searched for quite a while but I couldn't find even a simple backyard test of two systems running different media side by side.

If I had two little pumps I'd do the test myself tomorrow in some buckets.



And yes. Red scoria is safe as a grow bed media.

Im surprised this thread is as long as it is.

First: I only discovered Aquaponics like three weeks ago, so my practical experience is zero, none at all. Still thinking about building a first setup. I have been reading this forum like crazy though. Secondly: I'm not native English, so struggling a bit here.

That being said: Stuart, I wonder if your description of bio-slime is leaning a bit to much to the sealant-side of things... I would say that bio-slime would not block off even smaller pores, but rather act as a filter, allowing water and smaller particles to pass. Bacteria inside the pores would then add to the system. This would contradict your theory that not the total surface is important but more the voids between the media. We are talking very small dimensions here after all. But, again: just thinking out loud.....

By the thrust of the rest of your argument I think you mean the voids within the media granules rather than between.

As I said it is possible that "feed" for bacteria within clay walls and inside scoria pores covered by bio-film may be transported through the bio-film covering in some way. The things is we don't really know and there is now data to support the argument one way or the other.

While Wilson Lennards calculator is a useful tool it has its limitations. The bits that are based on his work we can assume are perfectly valid but the assumptions that he makes drawing on models developed to explain observations in constructed wetlands are less applicable if at all.

It has been a while since I've looked at his calculator but from memory the formulas that drive it are not available nor are the assumptions behind them. That makes it hard to assess the validity of his model. Especially since other than his own work with its limited range of configurations and loadings no trials have been run to test his models accuracy making it a potentially risky proposition to use it to extrapolate beyond his own work.

This was the quote/part of the theory I was contradicting. But maybe I am misreading here.

But I agree fully that this is largely a discussion based on logic and interpretation, not on hard data (those are usually the most fun anyway). There is also an argument to be made that because scoria and the like is formed so irregular the total of "outside surface"' is likely to be larger than when using regular shaped media, without adding the amount of "inside surface" of the pores. What I mean: maybe irregularity is more important than having pores. They just seem to always come together.

Yes lots of discussion, bombast, rhetoric, etc. with no way of actually reaching a conclusion.

As long as they stay nice they can be fun.

I'm glad for this thread, we pulled a bunch of shrubs out from the front of the house and there is a crapload of red lava rock I can harvest for AP media.

Is red scoria safe as a growbed media? Yes.
Washing scoria - I used red scoria, when I first set up I started washing with the hose, pointless exercise, way too much fine sand so I just filled the beds, the water ran red for approx a week till it all settled out in a thick layer the sump.
I have since gone back and emptied one gro bed (half Barrel) there was a huge area of solid sand/gravel mix in the bottom of the bed.
I washed this in a sieve (6mm mesh approx) submerged under water in a tank.
I will be doing this to all 8 beds as they become empty of veg because of the clogged sections.
I have just added another grow bed comprised of the top 340mm of an IBC, this took approx 6 hours to wash all the sand out the same way.
In my opinion it was worth the effort. The water ran clear within 2 hours. By the next morning there was a very light dusting of fine scoria on the bottom of the sump and crystal clear water.
BUT, I now feel safe in that there will be no clogged sections (at least from sand)

Some additional information, I'm not sure if it's been posted (look at pyroclastic Tuff section p. 76 ) - http://www.fao.org/hortivar/scis/doc/publ/8.pdf

I built some growbeds out of scoria long before finding this thread, and everything seemed to work out (although cleaning was a pain as others have stated).

My question though is about worms. The stuff is sharp! Does anyone have compost worms living in their scoria grow beds? Are they OK?

I do. They are fine.

Same here.

Worms and snails can walk over a razor blade without any trouble.

I saw it on TV so it must be true.

I have been thinking about using this. Seen a few posts on Craigslist locally giving it away. Not sure of getting that or buying newer stuff at $5 a bag

It is not like it goes bad. If it was used in a way you feel is appropriate to add to your system, I would scoop it right up! $5 a bag is silly. Usually you can find a bulk gravel place that sells it for $100 per cubic foot.