Washed Gravel

[Eli]

I read an interesting article in an organic gardening magazine recently about re-mineralizing soil with rock dust. Anybody heard of this? Huge yields over long periods of time. Some big farm in the US just re-mineralized their entire holding based on trial results. Most of soil's composition is.... ground up rocks right? Plant likey much. So is it for the sake of the pumps that all this gravel for grow beds is being rinsed off? It seems to me a savings of water and of benefit to the mini-culture to keep all that 'fertilizer' in the system.

[RupertofOZ]

Eli,
Common product used by a lot of other aquaponicers is "Min Plus".....
Available from most Bunnings stores....

Have pictures but haven't found a way in this forum to post them yet.

With regard to washing the gravel for the growbeds, the main purpose is to wash out any "fine" particles that might cause problems for your pumps...

Initially people washed their gravel to remove the silty sedimentation and discolouration of the water, but as you say it has become realised that dis-colouration is not a real problem, (unless concentration is that high as to deplete the oxygen in the water) and any fine silt/sediment tends to settle out over time.

Similarly, there are benifits in retaining some dust for the purpose of supply trace elements to the plants.

PM me if you want some links on the subject of rock dust

[Eli]

What type of product is min plus? A fertilizer? A grow bed media? Forgive my ignorance, I've spent hundreds of hours in Home Depot, but only about six hours in Bunnings (in the last three days though:)). Newbie to Australia, expect me to have problems w/ metric conversions as well.

[Eli]

Got the email. Right, crushed volcanic rock. I can't believe it wouldn't be great to keep all that rock dust in the system somehow. So how to settle it out for use without wasting water and without nixing the pump? In California they have a red volcanic pumice type rock that I bet would be a great grow media. It's for landscaping, maybe the mm diameter is too big. Do they stock that here?

[RupertofOZ]

Eli, a lot of people have been attaching an old sock, piece of old towelling or similar to the return line back to their system tank or sump....

That way most of the dust settles into the growbeds, the rest is "filtered" by the sock to prevent return into the tank and any possible damage to pumps, or sedimentation/discolouration

[Eli]

How about a double sump, so the overflow goes over the top into the pump sump?

[Murray]

Eli,

Here is a link to an Australian supplier of Mineral Rock Fert
http://www.mineralfertiliser.com.au/main.htm

I have used it on my system for about a year now. 1 cup per sq mtr of grow bed about once every 3 months. Maybe I am overdoing it a bit but I am sure it is working well, and will not do any harm...only good.
I just sprinkle it over the top of the bed and let it work it's way down. The Alroc stuff I use would not be a problem to the pumps. Some other types maybe perhaps as Rupert says.
The Alroc stuff is pelletised/granulated and looks just like a regular fert, except it is light grey in colour. Water quickly breaks the pellets down and it disappears into the system.
I feel that aquaponics systems benefit greatly by the application of the mineral rock dust.
Muzza

[Jonty]

Murray,

I'm happy I purchased some Alroc when I picked up my grow bed. In the goldfish pond/grow bed setup, the silverbeet was always green but not as deep a colour as the ones grown in soil. Tried some iron chelate but it made no difference. I used a small sprinkle of alroc on the grow bed and everyone remarks how great the silverbeet looks. (really dark green).

I also have a couple of bird baths but find the mickeys (noisy miners) are always at the blue barrel system for a drink. Maybe the water is sweeter with the alroc?

Have put some in the new system. Will continue to use it sparingly.

Regards
Jonty

[GaryD]

Hi Jonty,

I filled my new grow beds with 20mm blue metal......a gravel derived from basalt rock. It comes with its own rock dust.....lots of it......free!

I Googled blue metal and discovered that the rock dust has lots of the goodies that the more expensive commercial rock dust products have.

My first pH reading was 9.0.

I've since topped off the blue metal with a 50mm layer of 10mm drainage gravel.

Gary