List of aquarium safe rocks? - The Planted Tank Forum
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post #1 of 11 (permalink) Old 02-28-2015, 04:21 AM Thread Starter
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List of aquarium safe rocks?

Is there a comprehensive list of aquarium safe rocks anywhere?

Through research I have found that the following types are safe/won't raise pH, etc:


I'm also pretty sure volcanic types of rock are safe?

And limestone rocks are generally not safe due to leeching.

There are a lot of really beautiful rocks you can buy from landscaping supply companies that a) are less expensive than dedicated aquarium rocks, b) offer a lot more variety. So I was just wondering if someone had compiled a list somewhere to refer to. Or if I should bring a bottle of vinegar with me every time I visit a stone yard and secretly test. :-)

Bump: Of course as soon as I asked, found this:
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post #2 of 11 (permalink) Old 02-28-2015, 09:41 AM
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Not sure I have any more to add, but I'd like to comment on the quartz.
Be careful with quartz as it will often have "rust," "iron," and/or "copper" etc metals "infused" with it... I'm not a geologist but I'm sure you get the idea.
Good ole vinegar test though...
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post #3 of 11 (permalink) Old 02-28-2015, 02:22 PM
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post #4 of 11 (permalink) Old 02-28-2015, 03:49 PM
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You could bring a stronger acid to the store. Such as one of the reagents in the API nitrate test.

Scratch the rock. (Does it scratch easily? See the Moh test)
Put a couple of drops of your acid in the scratch.
Instant fizz: Use this rock only in a hard water tank.
Few bubbles, but it keeps on bubbling: Might be OK in a moderately soft tank, or one where the acid supply (peat, IAL, oak leaves, decomposition...) balances the few minerals this rock would add.
Couple of bubbles then it stops, or no bubbles: Good for all tanks.

Now take the rocks home and put them in a bucket of water treated the way you will for the aquarium. Monitor GH, KH, TDS, pH. If these change more than you like, do not use this rock in this set up.
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post #5 of 11 (permalink) Old 02-28-2015, 08:07 PM Thread Starter
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Thanks for posting that. It does seem to be in a bit of a contradiction with the article I found after my original post (see it in the "Bump" section). Sandstone isn't recommended by the Wiki entry and is so in the other article. If people are split on that, probably best to avoid it.

I'm really interested in rhyolite though. If you google stuff like "Apache Gold", "Apache Pink", etc. There are some neat options with a lot of character. Rhyolite is volcanic, so "should" be OK. Especially considering that volcanic rock, pumice, and obsidian are all considered safe. They're all volcanic rocks.

And speaking of obsidian, I'm psyched. I love the black jagged look. Might need some smoothing though... Tumbled would be great but tumbled is chemically treated during one of the stages. And even if you requested it tumbled only with water, they'd still probably use tanks that they use for the chemical treatment. Home tumbled maybe..

Another one I also love is jasperite. I think it's quartz based. And there is a blue quartzite I cannot recall the name of that also seems very attractive. Would be fun to go to some stone yards and play with the rocks. You can often take samples.
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post #6 of 11 (permalink) Old 03-01-2015, 12:51 AM
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A hard sandstone is usually safe, though a limestone parent material would make the sandstone good only in a hard water tank.
Soft sandstone would crumble in the tank, probably make a mess.

As sand got sifted into drifts long ago, sometimes the particles got separated by size, and some 'sand' stone is made of some very fine soil, more the particle size of silt. Often this is more solidly packed together, and more likely to hold up in the tank.

Pretty easy to tell in the rock yard: If it is already falling apart on the pallet, lots of dust and crumbs under the pallet, then it is likely to do the same thing in your tank.

If you take some baggies to the rock yard and a Sharpie pen you can take samples and label them, then test them at home.

Often the people in the rock yard have no idea what the geology of the rock is. They can usually tell you what state the mine is in, and occasionally a little more than that. But extensive geology or chemistry is beyond what they need to know to sell the stuff.

There is a local chert that is really pretty, and it is inert. The colors vary from almost yellow to deep maroon with thin white bands. Mostly it is a bit more purple than a rich brick-red. Hard to describe. Subtle enough that it is not a glaring RED, but rich enough to be distinctive.
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post #7 of 11 (permalink) Old 03-01-2015, 09:29 AM
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I don't know what else to say... there is so much confusing, and possibly straight-up-wrong information on those sites. One of the many flaws of the internet...

Most rocks won't straight-up kill your fish. Usually when people are worried about "aquarium-safe" rocks, they are concerned about rocks that may affect water parameters like hardness (GH, KH) and pH.

There are a lot of carbonate rocks (limestone, dolomite, travertine, tufa, coral, calcite, marble, and a few other terms I'm forgetting), that aren't poisonous or anything, but will react with tank water, dissolve slightly, and raise GH, KH, and pH. Most of these are some form of calcium carbonate(CaCO3), maybe some magnesium carbonate(MgCO3), or some mix of the two. Calcium carbonate is far more common. When these rocks are placed in water, a small part of them dissolves, releasing carbonate ions (-CO3), and magnesium/calcium ions (Mg+/Ca+). Carbonates will directly raise the KH(carbonate hardness) of your tank, and possibly react with any acids present, leading to a raise in pH. I'm a bit more ignorant on the chemistry of what happens with the magnesium/calcium ions (Mg+/Ca+), but at the very least, they will raise the GH (general hardness) of the tank. They are also important for plant and beneficial bacteria growth, so there should almost always be at least some of these in the tank.

If you have hard water coming out of your taps, this might not be that big of an issue, as people have been keeping (and sometimes even breeding) softwater fish in hardwater set-ups for some time now. On the other hand, if you are going for a hardwater fish, like rift-lake cichlids, or some live-bearers, then these rocks would pose no problems, and possibly some benefits for you.
If you are trying to maintain a softwater environment, and have soft tapwater (or are using RO/DI or pretreating with peat, or whatever...), then you should avoid these rocks.

This is a very broad generalization, but most igneous rocks will be safe for any tank-type. Granite, basalt, obsidion, rhyolite, lava rock, pumice, etc.

Most metamorphics are safe (gneiss, schist, slate, etc.), but some are potentially problematic (marble, and some others I'm not remembering right now...), and some will be straight-up toxic (mostly metal ores).

Sedimentary rocks are a confusing mixed bag... Usually sandstone is silica sandgrains in a matrix of... something? Silica is completely inert and fine for any tank setup, but the matrix can be any number of substances, and a silicate sand stone with a carbonate matrix isn't unheard of...

tl,dr; I'd avoid rocks with metallic or really bright colorings - might be a metal ore if you don't have more specific information. Like Diana mentioned, take something steel, and try to scratch the rock. If you can't scratch it, it's probably a silicate and fine for whatever. If you can scratch it - try testing it with acid (where you scratched it), if it bubbles, it's a carbonate, and should only be used if you have a hardwater set-up.

And try to ignore the names in petshops and stoneyards. They have about as much to do with the composition of the rock as my dinner did.
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post #8 of 11 (permalink) Old 03-01-2015, 03:04 PM
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Lochaber is throwing in some good info here even though it may make it sound confusing to many. But then he did skip over one on the even more confusing common rocks.
Conglomerate? A mix of rocks for short terms. So one rock can have several types?
What It gets down to in my use is that there can be no one list of all the rocks which are "safe". Even if we had a firm idea of which rock we held in out hands, the definition of safe changes when the water is different. As mentioned limestone is safe for me and I use it all the time. But that doesn't mean it is safe for you and your water.
It true that much of the hobby info is written on the East coast where there is soft acidic water and often it is written that limestone is not safe to use. So you have to check information to see if it is safe for you and your tank.
All this winds up meaning a list might be written but it does not mean it would be accurate.
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post #9 of 11 (permalink) Old 03-01-2015, 05:44 PM Thread Starter
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Hmm, thank you all for your great feedback. It makes sense that the chemistry of your water will determine what kind of reactive hardscape material you can put in it. I do live on the East Coast and my water is indeed slightly soft and acidic.

The nice thing about stone yards is that often times (but not always) you can find a great selection of what they refer to as "exotic rock" or "specimen boulder" that offers a lot more options for someone looking for a unique approach to hardscaping than you will find in any LFS. Even if you did buy online, most of the rocks offered are ADA types. Which limits you to like four/five kinds. Nothing wrong with those rocks, they are fairly nice but they don't give great many scaping options. And they cost way too much compared to what stoneyards will charge per lb. For example, I have in the past purchased Yamaya stone and honestly when I received it I was so underwhelmed- it's basically granite rubble or riprap as the stoneyards will call it. I won't even go into how much more expensive manually pocketed volcanic rock for aquaria costs versus naturally pocketed lava rock from stoneyards.

I do agree though that stoneyards aren't really savvy when it comes to this stuff. Some are better than others. There are places that can tell you what the geological origin of the rock is, and many others that haven't a clue. But they cater to a market that doesn't quite care about chemical specs in such detail.

The bottom line is, there probably are dozens of kinds of rocks we can use in our tanks, probably a lot more kinds than wood. In the rhyolite example, I see almost nothing offered for aquascaping, and that rock can have some incredible color and flow banding. So as hard as it will be to have some sort of general reference as to what's safe for what type of situation, I think it could benefit a lot of people in the hobby.

I also read that volcanic rock types may leech chelated iron in the water? Seemed to be an indication that this is beneficial to plants more so than a concern. I do know chelated iron is a great plant (aquatic/terrestrial) supplement that results in lush green foliage in proper doses. Can someone confirm/give some educated feedback on this?
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post #10 of 11 (permalink) Old 05-01-2017, 11:23 PM
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Thanks for the post!! This has been very educational. Could someone help me remember a name of a rock. It comes in larges pieces and it is Blackish with gray or white veins. It has a different name and I can't recall it. It is said to not change water params. I have a pic but doesn't look like I can attach it here. Also is zebra rock safe? Thanks
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post #11 of 11 (permalink) Old 09-12-2020, 08:12 AM
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I advise you Royal Imports Decorative Polished Gravel River Pebbles Rocks
Royal Imports 5lb Large Decorative Polished Gravel River Pebbles Rock

If you would like to shop for safe and natural rocks for fish tank, then this Royal Imports pebbles rocks will definitely be a great addition to your tank. This won’t only help make your aquarium look more attractive, but your fish and other invertebrates will surely love them too.

The common applications for this type of pebble rocks are for decorative concrete topping, flowerbeds, walkway paving, and groundcover. These are ideal pebble rocks that are deemed as an economical and permanent option to yearly wood composting.

These rocks are highly recommended for air plants too. They are comparably uniform in texture and size and they also come with an adequate variation which is specially intended to provide more uniqueness and appeal. These are softly polished and because of that, the colors stay real without much luster. The undertones are great to behold.

The colors of these pebbles are natural and mainly consist of diverse shades of black, white, and brown rocks. They are easy on the feet since they do not have sharp edges. They come in a wonderful combination or medium-sized and large non-toxic stones.

What is more, just like sandstone in the aquarium, they could serve as a very lovely embellishment to tanks, garden, flower arrangement, bird feeders, and many other interiors and exterior dcor purposes. The package contains sufficient natural stones for you to use.

Please be guided that you need to rinse them properly prior to adding them to where you intend them to be. This must be carefully done if you plan to add them to your aquarium.

1.Non-toxic and environment-friendly river rocks
2.Ideal for home decor and an artistic interior/exterior design
3.Excellent shapes that provide good drainage
4.Practical alternative to yearly wood mulching
5. Durable and does not deteriorate instantly
1.Have the tendency of forming molds
2.Slightly lusterless
3. Right to it, the reason why these rocks are a must-buy is that they come in many different uses. They are not merely for beautifying your potted plants, lawn, or garden but these are also perfect alternatives for your tank. For a fact, these are very well-known accents to tanks, terrariums, ponds as well as water gardens.
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