Is Lava Rock Good for Aquariums?

Lava rock has become an increasingly popular decoration and filtration media in home aquariums. Its rugged, porous nature makes it aesthetically pleasing and provides ample surface area for beneficial bacteria to colonize.

But is lava rock a good choice for your aquarium? This comprehensive guide will explore the pros and cons of using lava rock in freshwater and saltwater aquariums.

is lava rock good for aquarium

An Overview of Lava Rock

Lava rock forms when hot, molten lava from a volcano cools rapidly and solidifies. Air pockets and bubbles get trapped as the lava solidifies, creating a highly porous rock. Lava rock can be reddish, black, brown, or gray.

The porous nature and varied surface textures of lava rock make it attractive as an aquarium decoration. Lava rock can create caves, arches, piles, etc. The colors and shapes provide a naturalistic environment.

In terms of functionality, the pores and crevices make excellent surfaces for nitrifying bacteria to colonize. These bacteria convert ammonia and nitrite into less harmful nitrate. This makes lava rock a popular choice as biological filtration media.

Benefits of Using Lava Rock in Aquariums

Several benefits make lava rock a good choice for freshwater and saltwater aquariums:

Natural Appearance

The craggy, porous surface gives lava rock a very natural look. This allows you to create rock structures and caves that mimic natural environments. The colors blend in well.

Surface Area for Beneficial Bacteria

The porous nature provides abundant surfaces for nitrifying bacteria to grow. This makes lava rock effective as biological filtration media. More bacteria means better water quality.

Promotes Growth of Biofilm

Pores allow organic debris and mulm to accumulate. This enables growth of a biofilm containing microorganisms that breakdown waste.

Can Adjust pH Levels

Lava rock is chemically inert. But over time, water flowing through the pores can leach minerals that raise pH and hardness gradually. This helps buffer pH changes.

Provides Shelter for Fish

The cracks and crevices make perfect hiding spots for shy species like bettas. Piling lava rocks creates caves for fish to explore and take cover in.

Safe for Aquarium Inhabitants

Lava rock does not affect water chemistry rapidly. The inert nature makes it safe for fish, invertebrates, and live plants.

Long-Lasting and Reusable

Lava rock is extremely durable and long-lasting. It does not decompose or break down over time. You can reuse it in tank rearrangements.

Affordable and Readily Available

Compared to other rock types like dragon stone, lava rock is an affordable and easily obtainable option at most aquarium stores. This makes it beginner-friendly.

Adds Dimension and Creates Focal Points

Interesting lava rock structures protruding from the substrate can be used to add depth and dimension to aquarium layouts. Rock piles create good focal points too.

Suitable for Freshwater and Saltwater Setups

Lava rock’s versatility enables its use in freshwater community tanks, FOWLR, and reef saltwater aquarium setups.

Drawbacks of Lava Rock for Aquariums

However, lava rock also comes with some disadvantages:

Can Contain Harsh Minerals

Some lava rocks may leach minerals that rapidly affect pH and water chemistry. These should be avoided. Test each rock individually first.

Sharp Edges Can Damage Fins

The rough, brittle surface often has very sharp edges. These could tear fins of fish like bettas, angelfish, and guppies.

Difficult to Clean

The irregular shape and pores make lava rock difficult to clean once algae, debris, and gunk builds up. Toothbrushes are needed to scrub it.

Too Abrasive for Some Bottom Dwellers

The coarse texture and hardness of lava rock can scrape and irritate sensitive species like loaches and catfish that rest on the bottom.

Can Develop Anaerobic Pockets

Deep pores filled with debris can become anaerobic dead spots lacking oxygen. This can leach nitrites, hydrogen sulfide, etc. into the water.

Adds Significant Bio-load

The porous nature traps large amounts of debris that decomposes, adding to the overall bio-load of the aquarium.

Not Suitable for Cichlid Tanks

Lava rock is too rough and porous for African cichlids that prefer to dig through and sift substrate. It can scrape their body.

Can Ship with Manufacturing Dust/Residue

Some cheaper lava rocks may be covered with dust or oily residues from manufacturing or processing. This can pollute tank water.

Calcium Carbonate May Raise pH

Certain lava rocks might leach dissolved calcium carbonate into the water, making pH more alkaline.

Lava Rock Suitability for Specific Aquariums

Let’s take a look at whether lava rock is suitable for some common home aquarium types:

Freshwater Community Tanks

Lava rock works well in freshwater community tanks stocked with hardy species like tetras, barbs, danios, mollies, swordtails, etc. It provides ample hiding spots and surfaces for biofiltration. Start with smooth rocks and monitor water parameters.

Betta Aquariums

The many nooks and crannies make lava rock an excellent addition to betta tanks. Bettas appreciate resting spots and territories created with carefully arranged lava rock structures. Start with just a few smooth rocks as accent pieces.

African Cichlid Aquariums

Lava rock is too rough and porous for African cichlids that prefer sifting smooth sand substrate. Only use very smooth tumbled lava rocks sparingly in a cichlid tank.

Planted Aquariums

You can securely attach epiphytes like java fern and anubias to lava rock. But the hardness and sharp edges may uproot stem plants over time. Use lava rock mainly for hardscaping, not directly in planted areas.

Reef Tanks

Use lava rock mainly for structural purposes in FOWLR and reef tanks. Stacked forms make good shelter for shy fish. But the bio-load may be problematic in small reef setups. Monitor parameters closely.

Brackish Aquariums

The inert nature makes lava rock safe for brackish setups. But the hardness and sharp edges pose issues for species that burrow. Use just a few smooth accent rocks for hides and structure.

Turtle Tanks

Lava rock is too rough and porous for turtle tanks where smooth stones and driftwood are safer decor. Turtles may also try to bite off and ingest pieces of brittle lava rock which can cause impaction.

How to Prepare Lava Rock for Aquarium Use

Before placing lava rocks in your aquarium, they must be properly cleaned and conditioned to make them safe for fish. Here are the steps:

1. Rinse and Scrub

Rinse the lava rocks under tap water while scrubbing with a brush. This removes loose particles, dust, and surface debris. Check for oily residue or manufacturing contaminants.

2. Soak and Clean

Soak the rocks in a bucket for 1-2 weeks, changing the water periodically. This helps leach any soluble minerals and manufacturing residue.

3. Disinfect and Decontaminate

Disinfect the lava rock properly before use. Boiling for 5-10 minutes is ideal but you can also soak in a mild bleach solution. Rinse thoroughly afterward.

4. Test and Monitor

Test each lava rock separately in a container of water for 1 week. Monitor for pH, hardness, and chemistry changes. Discard any rock that rapidly alters water chemistry.

5. Smooth Out Sharp Edges

Carefully smooth out any sharp or jagged edges and points that could damage fins with sandpaper or a file. Round off the tips of pointed rocks.

6. Rinse Again Before Adding

Do a final rinse of the conditioned lava rocks before gently placing them into the aquarium with clean hands. Monitor water parameters closely afterward.

How to Use Lava Rock Effectively in Aquariums

Once prepped, lava rock opens up a whole range of possibilities. Here are some tips for using it effectively:

Start Slowly and Observe

Introduce just a few lava rock pieces at first. Observe any effects on fish and water parameters before gradually adding more.

Create Interesting Structures

Stack, arrange, and pile lava rocks to build caves, archways, stonehenges, ridges, cliffs, etc. These make fascinating focal points.

Use For Defining Territories

Strategically place small clusters of lava rocks to create visual barriers that define territories and break up line of sight for territorial fish.

Build Sheltered Zones

Construct sheltered areas like thickets and tunnels out of lava rock for timid species like bettas, dwarf cichlids, and shrimp.

Use in Dedicated Filter Chambers

Fill mesh filter bags with lava rock and place them in sumps, canister filters, and other filtration units to boost biological filtration.

Combine With Driftwood

Blending lava rock with branches, roots, and bogwood creates a more natural composition reminiscent of a stream or lakebed environment.

Attach Plants to Rocks

To create miniature landscapes, use aquarium-safe adhesives to attach mosses, anubias, bucephalandra, and ferns onto lava rocks.

Create Levels and Ledges

Arrange lava rocks on varying levels or create staggered shelves. This adds height and lets you separate species that prefer different tank levels.

Direct Water Flow

Position lava rocks to direct and concentrate filter outflow. This prevents dead spots and helps distribute nutrients to plants and coral.

Make Detritus Traps

Place lava rocks near the bottom or lower flow areas to collect decaying matter intentionally. The trapped mulm can be siphoned out during maintenance.

Mix with Other Rock Types

Combining lava with other rocks like quartz, petrified wood, dragon stone, etc. adds more visual variety and interest.

Ideal Fish for Lava Rock Aquariums

While suitable for most community species, here are some fish that especially appreciate what lava rock offers:

  • Bettas – The many nooks make perfect resting and hiding spots. Helps reduce aggression.
  • Gobies – They like squeezing into tight crevices and lava rock piles resemble their natural rocky habitat.
  • Blennies – Rock-dwelling species like peacock blennies appreciate the abundance of lava rock crevices.
  • Toadfish – Their drab mottled coloration provides camouflage when resting against lava rock.
  • Cichlids – Dwarf cichlids like apistogramma and kribs use lava rock hides and caves.
  • Plecos – Armored catfish like otocinclus, clown pleco, and bristlenose pleco graze on algae covering lava rock.
  • Loaches – Loaches like kuhlis, chain loaches, etc appreciate smooth lava rocks scattered on fine sand.

How to Clean Lava Rock

While lava rock is durable, it does require occasional cleaning to prevent excessive buildup of debris:

Siphon Gravel

Use a gravel vacuum during routine water changes to suck out debris collected within lava rock stacks and piles.

Swish in Bucket

Remove rocks and gently swish and agitate them in a bucket of tank water to dislodge debris before returning them to the aquarium.

Toothbrush Scrub

For tougher buildup, scrub lava rocks with an old toothbrush while holding them under running tap water or in a bucket.

Bleach or Vinegar Soak

For more thorough cleaning, soak the lava rocks in a mild bleach or vinegar solution for 30-60 minutes before rinsing thoroughly.


Use an aquarium gravel washer/power washer attachment to blast debris out of the pores with a strong water jet.

Replace Older Rocks

Over several years, very old lava rock becomes too clogged. Simply replace these older rocks with fresh ones. The old ones can be cleaned for reuse later.

The Consensus on Lava Rock: Should You Use It?

Lava rock offers some great benefits but also comes with a few cautions.

Use lava rock if: You are willing to monitor water quality, pick smooth rocks, and provide regular cleaning. The aesthetic appeal and functionality make it rewarding.

Avoid lava rock if: You want zero effect on water parameters, have delicate fish, or cannot provide maintenance.

The consensus: With proper selection, preparation, and care, lava rock can be an excellent addition to most home freshwater and saltwater aquariums. Its natural charm and functionality make it a staple among aquarists.

Using Lava Rock Safely in Specific Aquariums

While lava rock can work in most aquarium types, specific tanks require extra precautions and planning for its safe use.

Lava Rock in Betta Fish Tanks

Bettas appreciate the ample hiding spots and territories that lava rock provides. But their long, flowing fins are prone to tearing on the sharp edges.

Betta-safe lava rock tips:

  • Select only smooth, rounded rocks with no sharp points or jagged edges
  • Sand down any rough spots with fine grit sandpaper
  • Start with just 1-2 lava rocks and monitor betta’s fins
  • Place rocks on aquarium bottom, not protruding up steeply
  • Avoid stacking rocks too high or tightly packing together
  • Check regularly that betta’s fins are not snagging or tearing

Using Lava Rock in Planted Tanks

Lush planted aquariums often rely on nutrient-rich substrate. Lava rock alone lacks essential minerals for plant growth.

Lava rock in planted tanks:

  • Use lava rock mainly for hardscaping elements like caves, not planting beds
  • Combine with nutrient-rich substrate like Fluval Stratum under the plants
  • Attach epiphytes to lava rock decor using gel or superglue
  • Place smooth lava rocks around stem plants for anchoring versus sharp gravel
  • Periodically add liquid fertilizer to account for lava rock’s lack of nutrients
  • Ensure good water circulation to prevent dead spots behind dense rock piles

Lava Rock in African Cichlid Aquariums

The sharp edges and hardness of lava rock can injure African cichlids that constantly sift through substrate.

Making lava rock cichlid-safe:

  • Select only the smoothest tumbled lava rocks without sharp points
  • Sand down any remaining rough spots to prevent scraped skin
  • Use just one or two pieces as accent décor, not covering the whole substrate
  • Place rocks on bottom, avoiding tall structures cichlids can knock over
  • Combine with a child-safe smooth sand substrate for cichlids to dig through
  • Provide additional rock-free digging areas and terra cotta pots

Lava Rock in Reef Tanks

Some lava rocks’ high bio-load and alkalinity pose risks for sensitive reef inhabitants.

Using lava rock in reef tanks:

  • Test each rock thoroughly in separate container for 4+ weeks first
  • Monitor for water chemistry changes like pH spike or hardness increase
  • Use only inert, conditioning lava rocks that show no effect on parameters
  • Rinse meticulously and scrub all surfaces to prevent pollutants
  • Place rocks stable positions avoiding toppling over and damaging coral
  • Ensure excellent flow and circulation around rock piles to prevent dead zones

Key Takeaways

While lava rock can generally be used in most aquarium types, extra care and planning helps optimize safety and effectiveness:

  • Thoroughly research and test rocks first before adding to any aquarium
  • Select smooth rounded lava rocks and remove any sharp edges
  • Start with just a few pieces and gradually increase number as you monitor effects
  • Combine lava rock with appropriate substrate types for specific tanks
  • Ensure ample water flow around rock structures to avoid dead spots
  • Provide extra maintenance like vacuuming and scrubbing rocks when needed

With proper precautions, lava rock can safely enhance various home aquarium setups.