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Rocks that affect PH

16977 Views 6 Replies 7 Participants Last post by  PlantedRich
I don't know if this is in the right place or not, so if it needs to be moved, please do so.

I have been looking all over to find a list of common rocks we use in the aquarium, and the affects it has on PH. More specifically, what PH range each type will maintain in aquaria.

For example:

Texas Honey Rock:
Lava Rock:
petrified wood:
Lace Rock:

I know some of these will be inert, but I thought a list might help some people out, including myself! If anyone has experience, or knows the affect any of these have on PH, please note it. Also, if anyone can think of more, please list it as well. I may try to get pictures to go along with it as well, since some rock is called other things in different parts of the world!
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Petrified wood is usually made of silicates (like agate and quartz) and therefore is rather inert in a tank. Other chemical elements are often included such as iron which can give it lovely red and browns and copper which can give it greens and blues. These other elements are pretty locked up into the rock and don't leach out in any noticeable amount.
I've had a large chunk of nice agatized petrified wood with red and green in it for almost 30 years now and haven't had any problems. It's temping to turn it into slabs and cabs, but I've resisted so far.

Anther rock I use a lot in my aquariums is quartz. It's hard, pretty and inert.

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It's kinda difficult using names like that, since they aren't really official, and I've seen different types of rocks labeled with the same name.

Aside from that, granite, lava, and petrified wood are generally inert.

I believe Texas holey rock is limestone based, but I'm not certain. I think most lace rock is as well, but I've also seen a type of weathered igneous (andesite maybe? I can't remember) also called lace rock.

So, limestone will generally raise your hardness and pH. Most holey rock and lace rock will probably be limestone based, and also raise pH and hardness.

Igneous rocks (granite, basalt, lava rock, pumice, obsidian, etc.) are almost always inert/safe.

Metamorphic rocks are usually safe (slate, gneiss, schist, quartzite, etc.)

Sedimentary are more difficult, some sandstones and such are fine, but a lot have carbonates in them, which will affect pH/hardness.

Also avoid rocks with metallic-looking particles, or irridescent type effects - A lot of times these are related to compounds containing heavy metals, which while not directly affecting pH or hardness, can leach toxic compounds into the water.

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Holey rock is just limestone that has more holes than slabs of limestone. From there I would think it difficult to peg a number to the PH each might leave. Since limestone is just sediment, the amount and type of each sediment would seem to vary and then the final number would also depend on the PH of the water you start with and how often the water is changed or added.
My thinking runs that if you add a piece of really soft limestone rock to acidic water and leave it for a week, you get a different number than if you add a really hard limestone to a different water for months or years.
Since any given rock might have numerous varieties of different materials, I think there would have to be a far more precise definition of the rocks before you could assign a firm number.
I think of granite as a very hard rock so if I added it to 6. 5 water, I might expect to wind up with 6.5 but if it I added it to 7.8 I might also wind up with 7.8.
I think we know about trends of different rocks but not to the point that we can assign a PH range.

And then there is lots of variety in the definition of "lacerock"! Lava that has lots of small holes? Limestone with the same or something entirely different?
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