# Using volcanic rocks as a base layer



## Guibang (Nov 11, 2019)

So I grew up on a volcanic island and I've always been told volcanic soil is the most nutritious soil there is. As volcanic rock is porous and friable, under the action of erosion and pioneer plants a lava flow can transform into soil within a few years.

So I just had this idea that maybe using volcanic rocks as a base layer could be beneficial on the long run?

Has anyone ever tried it? What is your opinion on this idea?

*EDIT*: of course when I say "base layer" I mean a layer underneath the soil and gravel layers.
*Edit 2* : Maybe this way one could even aquascape. Using lava rocks to get higher and lower areas. Or would it get anaerobic anyway and thus not recommended?


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## hoppycalif (Apr 7, 2005)

Volcanic rocks would be rich in minerals, although most of the minerals would not be available to the plants. They would not supply nitrogen, which is essential for plant growth. I doubt that they would be any better than most other forms of gravel, but I'm not even close to being an expert on that subject.


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## mysiak (Jan 17, 2018)

I am using crushed lava rock as a cap over soil (2-5mm fraction). Per manufacturer it's inert substrate with trace amounts of iron. As hoppycalif said, it's as good as gravel from fertilisation point of view. It has some advantages over gravel - it holds together very well, so you can create slopes/hills quite easily, doesn't go compact and should be "airier" meaning better transport of water (and oxygen/nutrients) to/from the soil. However it is much lighter than ordinary gravel, so plants get constantly uprooted initially (I superglued larger pieces to the plants to hold them down). Also it is quite sharp, so bottom feeders might get injured.

I wouldn't use it as a base layer, but if you're OK with its disadvantages, it's interesting top layer with natural black color.

Chemical analysis of "my" substrate:


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## mistergreen (Mar 3, 2007)

Porous lava rocks could be good for filters and growing beneficial bacteria. Nutrient wise, it's locked up solid. Organic soil would be better to release nutrients for plants.


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## dwalstad (Apr 14, 2006)

Guibang said:


> *EDIT*: of course when I say "base layer" I mean a layer underneath the soil and gravel layers.
> *Edit 2* : Maybe this way one could even aquascape. Using lava rocks to get higher and lower areas. Or would it get anaerobic anyway and thus not recommended?


Because the lava rocks are inert (no organic matter), I think that you could use them--just like any rock--underneath soil and gravel.

I like to use lava rocks to attach ferns (Bolbitus) and Anubias. Plant rhizomes seem to grasp and attach very firmly to the lava. Grow well, too!


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## fpn (Jan 2, 2019)

Lava rock has a higher cec than gravel - eco complete is basically that. You can use it as an inert base layer e.g. if you want to build a hill / slope.

Also people do use it as a cap and it likely is better than plain gravel due to the higher cec.

Personally I am not a huge fan as it is very light / not so easy to plant in and very sharp. Definitely contributed some scratches in my acrylic aquarium. Also if used as a cap you may want to avoid some fish like coryes as they can hurt their bristles on the sharp edges.


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## tiger15 (Apr 9, 2017)

I use larva rock as a base to attach epiphytes, make hills to elevate plants and caves for fish to retreat. The rough and porous surfaces allow firm rooting of plants and interlocking of rock piles. But don't count on it to provide any nutrients, not even iron, as none of the minerals are biologically available.


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