Are Lava Rocks Good for Aquariums?

There are many kinds of aquarium hardscape available, and lava rocks are one of the kinds most often considered. But using many kinds of natural hardscape can be detrimental to fish depending on its chemical properties and where it was collected.

Are lava rocks good for aquariums? The answer is yes, lava rocks are good for aquariums. In fact, lava rocks are fantastic for aquariums, for a number of different reasons: 

  • Aesthetic beauty
  • Provides shelter for fish
  • Harbors beneficial bacteria
  • pH neutral for fish safety
  • Lightweight
  • Economical
  • Organic and ecofriendly 

There are many good reasons why someone might choose lava rock as a hardscape to enhance the looks and ecosystem of their tank. Read on to find out more about lava rocks and how they can benefit the home aquarium.

What is Lava Rock?

Lava rock (also known as volcanic or igneous rock) is rock that has been melted by extreme geothermal, such as a volcanic eruption. This molten rock then cools into a porous form of rock that is commonly found. In fact, lava rock is the most abundant source of bedrock on the planet. 

This is because the Earth itself was formed by the repeated eruptions of volcanoes, which eventually went on to form the Earth’s crust. As a result, lava rock is a plentiful source of hardscaping material for aquariums, terrariums, and is even used by landscapers.

Since home aquarium-keeping came into popularity in the twentieth century, lava rock has been a popular form of aquarium hardscaping, which is defined as the hard architectural elements of an aquarium’s aquascape, such as wood and stone, versus softer elements such as live plants. 

Lava rock’s popularity as an aquarium hardscaping material has somewhat waned during recent years due to a surging level of interest in other kinds of hardscaping rocks such as seiryu stone that have been popularized by international aquascaping competitions. 

Benefits of Lava Rock in Aquariums

Using lava rock as the hardscaping in an aquarium provides a lot of advantages over other kinds of hardscape. Here are some of the reasons that lava rock is good for aquariums: 

  • Aesthetic beauty: Let’s face it, natural hardscaping looks pretty fantastic, especially in a planted aquarium. Real rock and wood features in a tank help to emulate the natural environment of the animals, making them happier and making your tank look great. 
  • Provides shelter for fish: Many different kinds of fish and invertebrates are nervous or timid if left in the open. This is a common instinct in prey animals. Lava rocks act as a calming shelter for animals in the tank and also helps them set up individual territories by providing a visual marker.
  • Breaks up line of sight: In communities of moderately aggressive to very aggressive types of fish, hardscaping in a tank isn’t just to look nice, it’s also used as a way to break up lines of sight across the tank that might otherwise trigger aggression between fish. 
  • Harbors beneficial bacteria: Because of its porous nature, lava rock is capable of being a safe harbor for colonies of beneficial bacteria, which greatly enhances the quality of the water in an aquarium once established. With large colonies of beneficial bacteria, aquariums are able to contain more fish and still maintain good water quality.
  • pH neutral for fish safety: Most types of lava rock are naturally pH neutral, which means they will not shift the pH of the aquarium water one way or the other. For species of fish and invertebrates that are sensitive to pH levels, this is an important consideration when hardscaping a tank. 
  • Lightweight: Due to its porous nature, lava rock is naturally lightweight compared to many other kinds of rock and is easier to manipulate in and out of the tank compared to heavier types of rock, which might crack the aquarium glass more easily. Lava rock also does not greatly increase the weight of the loaded aquarium for load-bearing purposes.
  • Economical: Compared to many other kinds of hardscape such as driftwood or seiryu stone, lava rock is economically priced and can be sourced more easily while providing more tangible benefits.
  • Organic and ecofriendly: As Earth’s most common bedrock, lava rock is collected easily and is an organic resource that does not damage the environment like plastics can. Since it is an organic substance, lava rock is completely biodegradable and environmentally safe.

Drawbacks of Lava Rock in Aquariums

While there are many advantages to using lava rock in aquariums, there are some disadvantages too. Here are some drawbacks you might want to think about when considering lava rock for your aquarium hardscape:

  • Sharp and abrasive: Lava rocks can have a sharp and abrasive surface, which is both dangerous to fast-moving fish (which might bump into the lava rock if startled and injure themselves) or fish with long flowing fins that might catch on the rocks.

  • Trap debris: Because of their porous nature, lava rocks tend to trap excess food particles, fish waste, and other dirt in the aquarium and hold them, which can potentially decrease water quality over time if the rocks are not occasionally cleaned or at least rinsed off with dechlorinated water.

  • Can scratch or break glass: If you’re not careful installing lava rock, you can accidentally scratch the aquarium’s glass with its abrasive surface. Pointed pieces of lava rock can also crack the aquarium if bumped into its glass sides, so move lava rock hardscape with caution when performing installation or tank maintenance.

  • Other filter media can be more efficient: While lava rock is good at harboring beneficial bacteria, there are other forms of filter media that can hold more of this bacteria than lava rock can, and without lava rock’s other drawbacks.  

Things to Consider When Using Lava Rock in Aquariums

While lava rocks can be a good (even great) choice for hardscaping your home aquarium, there are some aspects of the rock that should be considered before deciding to purchase some for your tank. Here are some of the things you need to think about: 

  • Weight: While lava rock is significantly lighter than many other kinds of stone, it still adds weight to the tank, which means that if you have a larger aquarium, you need to make sure that the aquarium stand or whatever piece of furniture it is displayed on is strong enough to take on the added weight.

  • Water displacement: While lava rock adds territory in the form of landmarks to an aquarium, it does detract from the overall volume of the water column that the fish actually get to swim around in. Make sure you don’t get so much lava rock you overcrowd your fish.

  • Fish type: If you are keeping fish that have long flowing fins, such as bettas, or fish that tend to dart around or race the tank either when interacting amongst themselves or when started by people passing the tank, you might want to consider another form of hardscaping other than lava rock, as it is not suitable for these fish.

Aquarium Animals That Like Lava Rocks

Many kinds of aquarium fish can benefit from having hardscape like lava rocks in the aquarium, but two groups in particular really enjoy an aquascape that centers around lava rock: 

  • African cichlids: One of the more aggressive types of tropical fish kept in the home aquarium, cichlids are known for both their territoriality and their bright and flashy coloring in dozens
    of hues and patterns.

    African cichlids are unique among aquarium fish in that they prefer hardscape-only aquascapes such as lava rocks or broken pottery arranged into caves rather than planted environments due to the elements at play in their native habitats.

    Because African cichlids prefer to set up territories in rock caves, a hardscape of lava rocks is a good option for a cichlid tank. It doesn’t disrupt the tank’s pH (which cichlids can be notoriously vulnerable to), and a lot of it can be used in a large aquarium to set up an elaborate cave system suitable for lots of cichlids in close quarters.
  • Freshwater shrimp: Freshwater shrimp are small invertebrates that come in a variety of beautiful colors and patterns, and

    Lava rock is beneficial for freshwater shrimp in a few different ways. The first is that lava rocks act as a good place for shrimp to forage for both detritus and algae, both popular food sources for them.

    Freshwater shrimp are also very sensitive to water quality as a general rule, and hardscaping a shrimp tank with lava rock can help with this due to the amounts of beneficial bacteria the lava rocks can harbor.

    Finally, lava rocks give smaller or juvenile shrimp a place to hide from their larger companions. Shrimp have been known to prey on each other, and if you keep fish and shrimp in the same tank, baby shrimp will certainly be subject to predation from your fish if you don’t provide them plenty of places to hide. Lava rock is a great option for this. 

Lava Rocks and the Nitrogen Cycle

One of the main reasons that lava rock is so popular is because it aids a tank in the nitrogen cycle. A nitrogen cycle is what allows an aquarium to be maintained as an ecosystem that can sustain living aquatic organisms, as their own toxins would otherwise build up in the tank and kill them. 

The nitrogen cycle is how aquarium keepers emulate the process of water purification in the natural environment, where nitrifying bacteria in the water convert biological waste such as ammonia into nitrites, which other forms of bacteria then convert into nitrates. 

Lava rock acts as a porous surface for these colonies of nitrifying bacteria to live in. Because bacteria can penetrate deep into the rock, the surface of it can be occasionally cleaned or rinsed off without hurting the lava rock’s beneficial properties. 

Without an established nitrogen cycle and filtration in place, aquarium fish will succumb and die of ammonia poisoning within just a few hours. Ammonia is toxic to fish in very few parts per gallon of water, so it doesn’t take much to wipe out the tank. That makes lava rock an important resource for anyone looking for a stable aquarium and good water quality. 

Alternatives to Lava Rocks in Aquariums

If a person wants to keep a piece of hardscape purely for colonizing nitrifying bacteria and not for aesthetic purposes, lava rocks can also be used as a filter media and kept inside a canister filter where they can’t be seen. That allows a person to get the benefit of them without having to use them as decoration. 

For the purpose of water filtration, there are a few alternatives to lava rock as a filter media that can be used inside a canister or hang-on-back (HOB) filter: 

  • Ceramic rings: Ceramic rings provide a better surface area for nitrifying bacteria than lava rock does, but their inorganic shape means they’re generally unsuitable for any kind of decorative hardscaping.

  • Bioballs: Bioballs are another form of manmade filter media and have become quite popular since their introduction on the aquarium market due to their efficiency in establishing colonies of beneficial bacteria. 

As far as decorating with lava rock, there are several alternatives that an aquarium owner can look at when deciding what materials to use as their hardscape. Here are some of the popular alternatives to using lava rocks in an aquarium: 

  • Manzanita driftwood: Manzanita driftwood is the driftwood of the manzanita tree and is regarded by many aquarists as one of the best driftwoods for aquarium decorating due to its dramatic shapes and density, making it a durable piece of wooden hardscape that does not easily succumb to algae or age.

  • Seiryu stone: Seiryu stone is a type of rock hardscape popularized by the Iwagumi style of aquascaping. Compared to some types of hardscape, seiryu can be rather expensive but does offer a beautiful, dramatic look. It’s important to note that for anyone wanting to use seiryu stone, it is alkaline and will alter the pH parameters of the aquarium’s water.

  • Dragon stone: Dragon stone (also known as Ohko stone) is another aquarium landscaping stone that has gained recent popularity due to its use in competitive aquascaping and is actually a clay-like material that is brittle and easily shaped. 

Where to Get Lava Rocks

Lava rocks can be obtained from a variety of places, depending on whether you’re willing to have the rocks shipped to you or not. Here are some of the places you can buy lava rocks:

  • Online specialty vendors: There are many websites on the Internet that specialize in hardscape for aquariums, and you can often find some very nice (if sometimes pricey) focal points for your aquascape here. Because these are often smaller shops, shipping can sometimes be a bit higher than in large markets like Amazon.

  • Large online markets: Markets like Amazon and eBay feature a dazzling array of aquarium hardscapes for sale, and you can also get a wide range of prices available too to fit every tank budget.

  • Local pet or aquarium supply shops: Big box pet shops such as Petco or Petsmart have a somewhat limited selection of aquarium hardscapes in comparison to local fish shops, so check your local aquarium supply store if one is available to you. You can usually get a much better selection of aquarium decor at a store dedicated to aquariums. 

How to Install Lava Rocks in Aquariums

Before you add lava rocks to your aquarium hardscape, you’ll want to do a little preparation on them first to avoid any problems during installation. To get the best results when adding a lava rock to your aquarium, follow these steps:

  1. Fill a bucket with dechlorinated water and rinse the lava rocks well. Take a brush and scrub the rocks clean, rinsing them until the water becomes clear. This is to remove any dust or other foreign debris that might be clinging to the rock that will cloud your aquarium or potentially hurt your fish.

  2. Put a cushioned aquarium mat or Styrofoam sheet under the tank. This will prevent pressure points caused by the uneven weight of the aquarium hardscape from causing cracks and potentially busting the aquarium.

  3. Add substrate before adding hardscape: Hardscape will easy scratch or crack aquarium glass if not handled carefully, so to prevent any damage to the bottom of the tank, put down a layer of substrate such as sand or crushed coral to cushion the tank’s glass bottom from the bare lava rock, which has a naturally sharp and abrasive surface. 

  4. Make sure rocks are stable: When stack lava rocks in the aquarium as cave structures, make sure that the rocks are completely stable and will not fall over. This will prevent fish from being injured or trapped, and also prevent one of the rocks from falling against the aquarium’s side glass by accident. 

Lava Rocks Are a Good Choice for Aquariums

There are a few disadvantages to using lava rock that have to be considered or mitigated, but overall, lava rock is a cheap and beautiful way to both decorate an aquarium and add a source of nitrifying bacteria that can keep an aquarium’s water quality healthy. 

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Adam Edwards
Hi, my name is Adam and I'm an aquarium enthusiast! I didn't discover the joys of being an 'aquarium fanatic' (as some of my friends call me!) until I was in my 20's. When I first started out I found it difficult to find all the information I needed so I started this website to compile all the useful information I can think of. Enjoy!