Can You Use Basalt in Planted Aquarium?

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Aquascaping is quite an expansive field as it’s an integral part of aquarium keeping. A variety of elements are used in the aquascaping business, but rocks form the backbone of any reliable aquatic layout. They provide the fish with hiding areas, offer anchoring support for plants, and create a more natural-looking environment.

Among the many types of rocks available for aquascaping today, there’s one type that stands out the most – basalt rock.

Is Basalt Safe for Fish Tank?

Yes, basalt rocks are safe to use for fish tanks, thanks to the material being inert. In other words, it doesn’t alter the water’s chemistry or overall quality. But what is basalt to begin with? Basalt rocks are formed of molten lava and are different than your regular volcanic rock, although not by much.

The notion of volcanic rocks describes a category rather than a specific piece. This category refers to all types of volcanic rocks resulting from cooling magma, no matter their mineral content. Basalt rocks make for a specific type of volcanic rocks with a specific mineral content. They are low in silica, contain less than 20% quartz, and come with a mix of biotite, labradorite, olivine, and other exotic elements.

Unlike regular volcanic rock, basalt rocks showcase a less porous surface, as they appear fuller and harder. They’re also impressively heavy, to the point where it will impact the aquarist’s ability to perform adequate aquascaping.

Does Basalt Change pH?

Basalt rocks are considered igneous rocks (‘fiery’) and do not alter the water’s pH or overall chemistry. However, this is only true for basalt stones used in aquascaping. In reality, basalt is even used in agriculture for its, you guessed it, ability to alter the soil’s pH.

Fortunately, the devil is in the details. The type of basalt used in agriculture comes in powder form and is generally used in conjunction with fertilizers to increase soil pH and enrich the soil with various minerals. These include calcium, potassium, magnesium, and others.

In compact form, basalt doesn’t leak any minerals into the surrounding environment, so it’s safe to use for aquariums.

Are Basalt Rocks Good for Aquascaping?

Yes, basalt rocks are great for aquascaping, so long as you can fit them within your system. It’s worth noting that basalt rocks are different from your regular aquascaping rocks for various reasons. These include:

The high density – Basalt rocks are generally smooth and dense with no visible porosity, holes, or crevices. So, plants may find it a bit more difficult to latch onto the rock’s surface at first. Porous rocks also serve as home for various cultures of bacteria inhabiting their many crevices. Basalt rocks don’t fit that category.

  • The esthetic impact – Unfortunately, basalt rocks are rather dull when compared with other, more vivid options. All basalt rocks display varying shades of grey and black, which doesn’t add too much diversity to your aquatic layout. Fortunately, the rock’s duller coloring can actually create a beautiful contrast with the fish and plants in a high-tech aquatic setup. So, it’s a double-edged sword, depending on your goals and vision.
  • The weight – Basalt rocks are heavier than your regular volcanic rocks. The reason for that is the rock’s increased density, unlike porous rocks, which are lighter overall. This can create difficulties during aquascaping, especially if you have an aquarium made of thinner glass. The tank cleaning process is also trickier since moving the rocks to clean around or under them is no easy task. The same issue becomes evident when restarting the tank and a complete overhaul is necessary.
  • The sharp edges – Many aquarists polish their rocks before adding them to the tank. They do so to smoothen any sharp edges that may cut or graze long-finned fish like bettas and angelfish. The problem is that you can’t really do that with basalt rocks. This is due to the stone’s density and hardness, making it difficult to work on.

Other than that, basalt rocks are great options for your tank. They provide a sturdy base for your plants, offer a great visual contrast with more brightly-colored elements like fish, plants, and other decorations, and are inert.

Just make sure that your tank can hold them, and remember to pressure wash or even sterilize them before use. It’s not uncommon for basalt rocks to carry various pathogens or chemicals into the tank and poison the environment. This isn’t a problem specifically linked to basalt rocks, but any aquatic component being added to an aquarium in general.

Can You Grow Plants in Basalt Substrate?

The right answer to this question comes in 2 forms. On one hand, we have basalt rocks which are inert. In other words, they won’t leak any minerals in their surrounding environment. They are also large, hard, and unfit to use as substrate. From this perspective, no, you can’t use basalt rocks as substrate for your plants.

On the other hand, basalt is being used as a nutritious substrate in powdered form. When crushed to dust, basalt actually transfers various nutrients to its surrounding environment. It will also influence the pH of the water or soil in which it is kept. The problem is that this only applies to agriculture. I am unaware of any instances of basalt dust being used as a plant substrate in life aquariums. So, don’t even bother with it.

Instead, you should stick to normal substrates to provide your plants with adequate support. The substrate you’re choosing for your plants should:

  • Provide adequate nutrition – Enriched soil is the best in this sense. It offers plants plenty of nutrients, eliminating or, at least, diminishing the need for additional fertilization. If you’re relying on inert substrates like gravel or sand, additional fertilization is necessary to keep your plants well-nourished. So, consider using root tabs to complement your inert substrate of choice.
  • Provide proper anchoringGravel doesn’t provide much of an anchoring support due to the particles being too large. Sand, on the other hand, is too fine, causing it to become compacted and strangling the plants’ roots. These come with different problems and require different solutions and approaches. You should provide your plants with proper anchoring support until their roots develop well enough to take over the task.
  • Be easy to cleanSoil has great nutritional value, but it’s difficult to clean properly. Sand is more compact, keeping all the dirt at the surface, so it’s easy to remove. The problem is that sand forms anaerobic pockets, which can release ammonia into the environment. Gravel looks nice, but the fish waste and food residues will often slip through the larger particles. Choose wisely and be wary of the differences between the various types of substrates.


Basalt rocks make for a great addition to any aquatic setup. They are hard, inert and create an interesting aesthetic contrast with the surrounding environment. Just be wary of the rock’s density and weight to prevent any potential accidents along the way.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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