Backyard Aquaponics
A place to discuss aquaponics

while i was reading Wilson Lennard web article on his site, i noticed the following, Quote " Correct Gravel Type

Gravel comes in many shapes and forms, and few people state which gravel is good or bad. For example, I visited a backyard system recently where Red Scoria was used. It was very dusty, very red, and was staining the pipe work. In addition, the Scoria has very sharp edges, which is no good for hands or plant stems. However, the owner could see no problem with this, and was happy to feed the plants and fish to his family. Many gravels may contain toxic chemicals and compounds, like heavy metals. Therefore, choose gravel carefully and correctly!''Unquote.
(http://www.aquaponic.com.au/backyard.htm).

So, exactly what are the 'toxic chemicals and compounds'? can anyone shed lights on?

Not sure peashoots.... email Wilson and ask him

Seriously, I know that gravels aren't gravels as Worms (i think it was) can attest.... he got delivered some gravel intended as road base...

Obviously had something mixed into it....

Probably depends where you get your supply I suppose.... maybe the "red" scoria has been artificially coloured or colour "enhanced"....

Peas shoots, F&F uses scoria i have scoria in my bed also. it somes in quite a range of grades, mine is smaller and rougher than F&F's.

have not kown scoria to be high in heavy metals

here is a composition of black scoria

SiO2 45-50% Al2O3 13-15% Fe2O3 32-4% FeO 4-6% CaO 5-8% MgO 4-6% Na2O+ K2O 4-6% TiO2 1-2% SO3 0.01-0.02%

i think there may have been a post here that had the composition, but i don't know..................

Nice of wilson to elaborate on which gravels and which chemicals

just lookign at that, it might be evident now why dads system originally displayed Fe defficiencies but has since come good........lots of Fe2O3, some time for anerobic areas to estabish................niiiice

Steve,

I too red scoria in my system. I am just a little bit scared after reading that.

i googled quite a bit with

scoria chemial analysis

scoria composition

couldn't find much

we'll have a look around................

makes me laugh, i wonder if said person ensured that his floating raft polystyrene did not contain halogen flame retardants ............

Rupe,

good answers.

It's pretty ambiguous and a bit alarmist...

He doesn't actually say that red scoria HAS toxic chemicals in it....

Just says "Some gravels have ....."..... like Steve says, not exactly helpful

Does your system run red and stain like he suggest the system he saw did?

nope, is mined as either red or black scoria. depends on the region i think

Hear you Steve, but I've seen stuff sold as red scoria at nurseries which didn't really look like scoria to me.....

But was a real nice colour and would have looked great as an edging

Would tend to think that any scoria running red in an AP system, even brand spanking new, would probably suggest that it was poor quality, badly stored or the bottom of the batch and was a LOT of dust in it, and would settle out in a few days anyway....

Sounds a bit exaggerated to me...

from http://www.burdetts.com.au/wwwroot/scoria.htm

Used for drainage, for decorative purposes in the garden and for hydroponics (growing plants without soil). It is either red, plum or black colour.

Rupe, my system initially was like that but the dust soon settled. now the water is crystal clear.

just wonder if the system owner he has visited was a member of this forum.

Even "normal" gravel and hydroton clay balls will run some sediment or colour for a couple of days....

Depends how well you wash it as well..... ask Les

so, provided all the gravels and scoria are the correct types, it would be good to mix them or use growbeds with different media in a system to reduce the chance of iron deficiency.

Ok, never let it be said that steve doesn't do the hard yards!

Here is an exhaustive list of the composition of A scoria

in my reading i found references that scoria was sometimes refered as volcanic rock..............after seeing the list of trace elements, i don't think i'll be bothering with any supplement rock dust..............

the major components are in % the trace ELEMENTS are in ppm