# Decomposed Granite



## pikachux3 (Feb 1, 2013)

I'm not exactly sure, but I know DG is commonly used in bonsais because of their rich mineral content.


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## Diana (Jan 14, 2010)

DG is pretty much inert. Not a lot of minerals that are available to the plants. 
Might need some serious rinsing! 

Around here the DG is either blue-grey (local quarry) or gold (2 different products, both shipped from about 100+ miles away). 

There is another material that looks similar, but I do not know the parent rock. Maybe granite. This one (IMO) would make the nicest substrate. It is a softer, deeper brown with some grey mixed in. More natural looking than the others. 

Red lava is also available in the same texture as DG, with fines or without. I use it as a media for bacteria colonies. I get the one without the fines, and even that way it REALLY needs the washing!

If there is any way of getting a sample (perhaps a torn bag?) you could run some tests, and look at the material when it is wet. See if it will work for you.


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## yashmack (May 20, 2013)

I think it will work, it has the right texture and look for what I would be satisfied with, im just curious how well it works as a plant substrate

here is the product page:
http://livingearth.net/products-services/products/landscape-sand-gravel
just looking at this page I can foresee a nice shopping trip for rocks and gravel pretty soon, hehe
is flagstone safe for aquariums? lol

and a pic of the granite:









how porous is this stuff is what im wondering
if its porous enough then root tabs and liquid ferts will probably make this a sufficient budget minded soil...
would having a layer of pete moss as the bottom layer help any?


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## DogFish (Jul 16, 2011)

If you do use it please journal your experience. I'm curious about how much/fast it will continue to degrade underwater. Worse case you end up with DG sand.


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## yashmack (May 20, 2013)

I will definitely be sharing my experiences
Unless I get someone here telling me a good reason to not at least try it I will be seeing how much a 40 pound bag costs next weekend


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## Fishermike (Feb 24, 2013)

The main issue that I'd be concerned about is that the mix of "fines" (silt and sand) and larger pieces tends to compact to a nearly solid substrate. This is actually by design - that's why it's used so much in landscaping, for mulch, paths, and driveways/motorcourts. It's very solid underfoot, unlike sand or pea gravel, and is an excellent weed barrier.

If you have lots of vigorous, well rooted plants, this might not be an issue. Just thought I'd mention it.


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## yashmack (May 20, 2013)

i was thinking the same, was going to sift the really fine stuff and maybe leave it out, or i might wind up mixing it with something else I find there
they have lots of stuff not listed on their website so i might find something cool  (expanded shale or calcined clay would be amazing...)


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## lochaber (Jan 23, 2012)

Granite is primarily mica, feldspar, and quartz (a few other things, but those 3 are the vast majority of the crystals/minerals present).

mica decomposes into clay first, and then feldspar will also decompose into clay. Quartz will eventually break down into smaller pieces (depending on how big the crystals were to begin with), but won't change into anything else.

depending on how decomposed it is, you probably either have clay mixed with feldspar and quartz, or clay mixed with quartz. No clue whether they do any processing like crushing/grinding, sifting, etc.

I can't see anything harmful, but I don't think there would be all too much benefit either...


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## yashmack (May 20, 2013)

lochaber said:


> Granite is primarily mica, feldspar, and quartz (a few other things, but those 3 are the vast majority of the crystals/minerals present).
> 
> mica decomposes into clay first, and then feldspar will also decompose into clay. Quartz will eventually break down into smaller pieces (depending on how big the crystals were to begin with), but won't change into anything else.
> 
> ...


The benefit is a cheap substrate, probably cheaper than gravel and im hoping more plant friendly than straight up gravel
I dont know the CEC of decomposed granite though or what minerals it might contain
Im wondering how porous it is as that will help it retain added nutrients and help give plants a better medium to grow in
I also like the color

i was hoping someone had used it before, but it doesnt look like it
I found one old post where someone had a mix of decomposed granite and sand growing plants but it was a question about algae, lol


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## yashmack (May 20, 2013)

Im going to be adding links to articles and forum posts ive found with some info on decomposed granite, hopefully this will be help to others with similar questions

Useful info on mineral content:
http://bogi.org.au/rock-minerals


> Granite
> 
> Crushed granite and naturally decomposed granite (aka deco) provides potassium, calcium, and magnesium. They also provide many other valuable trace elements such as silicon and iron. Reference the Granite wikipedia entry for a worldwide average of the chemical composition of granite. Note that deco often contains fine clay particles, so it is best worked into the soil (really as with all rock minerals).


Used for an aquarium substrate:
http://www.aquariumlife.com.au/showthread.php/47268-Tombolo


> Bottom layer - decomposed granite, dressed with pool filter sand and aquasoil around the edges.
> Next comes the zeolite, which I soaked in a weakish Seasol solution. This is my substitution for blood and bone. I will be adding ferts and co2 in this tank, so that extra organic element shouldn't be missed. Besides, I'll only be planting sparing in the sandy areas.
> Next came another layer of decomposed granite over the top.


http://www.wisegeek.com/what-is-decomposed-granite.htm


> Decomposed granite is a fairly environmentally friendly choice because it is a natural product, is permeable, and provides hardscape that requires no water. After the granite is in place, it will continue to weather, which adds beneficial nutrients to the surrounding soil and plants.


http://forums.gardenweb.com/forums/load/aquarium/msg071108133275.html


> I have used crushed granite before with much success. I get it from a farm and feed supply. A 50lb. bag is about $6.50US. It is a feed supplement for poultry. It is sometimes called Chix-Grits or Grani-Grit. Get the size that is about 2mm in size, I think it is sometimes called "grower" size. The color is mainly white to dark grey with some pink, depending on where it comes from. Granite is inert and wont buffer your pH. That is a concern with most pea gravels (at least the ones in my area locally). You could mix a bag of Schultz's with it to give it some nutriens for root feeders like amazon swords. That is really not neccessary though. The fish poop and other organics will make it quite rich in nutrients. For fertilizer supplements I would reccomend using hygroponics ferts and mixing it with water. A friend of mine sells small bags of all the nutrients you need and mixing directions. It will give you years of use and only costs about $10US or so.


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## lochaber (Jan 23, 2012)

I'm not certain how well it will provide those minerals to plants. Sure, the minerals are in there, but they are often bound up in the crystal lattice, and not available like the ferts we add as salts. I get the impression that a lot of people look at the chemical composition of a given substrate, and think that all those compounds are available, when they are no more available to plants then the oxygen in sand (SiO2) is to us.

Also, as to decomposed granite continuing to decompose, that won't noticeably happen in our lifetime, or even the lifetime of the next few generations.  

anyways, the clay part of it should have decent CEC values, so there's that.


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## yashmack (May 20, 2013)

thats what I was thinking too, its not as good as some of the soils available out there but it seems like it could be a good start
Im going to see what I can find to mix with it and help it out a bit too and of course I will be adding fertilizers if the plants dont seem to like it

It is a pretty proven substrate though, it is used frequently and with great success with Bonsai trees...
I found it on a bonsai website and looked into it, thats what got me thinking of using it in the aquarium


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## Diana (Jan 14, 2010)

I think it has too much fines, and will either cloud the water or compact. 

We use it to make walkways and it sets up almost as hard as concrete. It would not be my first choice as a possible substrate for an aquarium. I have access to a lot of free materials, (leftovers from jobs) and have used several similar products (sands, gravels and blends) in aquariums. A certain amount of fines is good. Clay has high CEC. But the coarser materials keep open the channels for water movement and roots to grow through. If that is the only material you can get, then I would sure sift through it to end up with not more than about 10% fines/clay, and aim for the rest to be anything from fine sand (somewhat gritty) on up.


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## DogFish (Jul 16, 2011)

Looked at this a little more. You do realize if you use this stuff your going to end up with a top layer of small pebbles...Right? All these "fines" everyone seems concerned about will settle eventually to the bottom.

I'm sure this product does make excellent walk ways, but that's not under water. I think the point is moot in this discussion.

lochaber's point is spot on having minerals is one thing, those minerals being available to use is quite another. 

If budget is you concern 40#s of playsand is $4 here, PFS goes for $8 for 40#s. If it's more about color you could sieve out the pebbles.

You can use root tabs or use sand as Cap over dirt. Either works well, both are proven methods.


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## yashmack (May 20, 2013)

its more for the aesthetics and partly for the budget. I dont like sand its a bit too fine and doesnt have large rocks.
Since its used successfully for bonsais I figured that there must be at least a portion of the minerals available to the plants or else it wouldnt be used.
As for the fine grains and clay, im going to go down to the company (possibly this weekend) and take a look at it, run my fingers through it and see what its actually like and how fine these particles are
Im fully expecting it to compact which we dont want so I will either sift it or mix it with something else to help it out a bit and open it up, will have to see what works when i actually get my hands on some
I dont know the cost but im sure its cheap as everyone has said so i would be more than willing to buy a bag for 5 bucks and run some experiments, just to get some answers as no one has any experience with the stuff in aquariums except for the handful of links I posted above...

Im keeping all this in mind, and I thank everyone for the info
Once I get a bag I will share my experiences with it here


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