How to Prepare Lava Rock For Your Aquarium (Step-by-Step Guide)

Lava rock makes a great addition to your aquarium. It lends a great natural look to your aquascape. Plus, it’s lightweight and easy to stack, so you can make some really cool caves out of it.

And lava rock is the perfect home for beneficial bacteria that will help process fish wastes, improving your water quality.

But, lava rock should be cleaned and sterilized before it’s put in your tank to make sure harmful bacteria don’t hitch a ride into your aquarium.

Today, I’ll go over the basic steps on how to do this.

How to Prepare Lava for an Aquarium

Lava rock inside planted aquarium

First off, you’ll need to clean off any dust or dirt that’s on the surface of the lava rock.

This kind of rock can really hold onto a lot of dirt because the surface is so porous. Getting it clean is really simple. 

You’ll need:

  • Plastic bucket
  • Plastic bristle scrub brush 
  • Tap water 


  1. Place your lava rock in your bucket and run water over it until the water runs clear.
  2. Scrub all the surfaces of the lava rock with the scrub brush.
  3. Run water over the lava rock again until the water runs clear.

Do not ever use soap to clean something that goes in your aquarium. Soaps can leave harmful residues that are toxic to fish!

Now that the dirt and debris are scrubbed off, the next step is to sanitize the lava rock.

DO NOT try to boil or bake lava rock (or any kind of rock, really). Pockets of air inside the lava rock can expand, causing the rock to blow apart. This can lead to injuries and/or property damage.

You’ll need:

  • Plastic bucket
  • Plain bleach (sodium hypochlorite) – DO NOT use scented or splashless bleach
  • Dechlorinator 
  • Tap water 


  1. This is best done in a bathtub or shower and be sure to wear clothes you don’t mind getting bleach on.
  2. Mix 1 part bleach to 20 parts water. You’ll need enough of the solution to completely submerge the lava rock in the bucket. 
  3. Place the lava rock in the bucket with the bleach solution and let it soak for about an hour. Bleach works on contact, but you want to give it time to work its way down into all the pores and crevices.
  4. Dump the bleach solution and rinse with tap water until you can no longer smell bleach.
  5. Submerge the lava rock again and add dechlorinator at 5 times the normal rate for that volume of water. Let that soak for about an hour, again to make sure that the solution gets down into the pores.
  6. Dump the water and let the lava rock air dry. 
  7. Once it’s dry, it’s safe to place it in the aquarium.


Lava rock is a great material to use as an aquarium hardscape. Not only is it beautiful, but it’s also a great home for beneficial bacteria.

But, lava rock that you buy can have lots of dust and dirt on it, and if it’s been sitting outside at a landscaping store, could potentially harbor harmful microorganisms.

Luckily, it’s super simple to get it cleaned and sanitized. Just do not try to boil or bake it. This can cause the rock to explode, which can get someone hurt.

Soaking the lava rock in a bleach solution is much safer and will sanitize it quite nicely.

I hope you find this article helpful.

I wish you and your fish the very best!

Katherine Morgan
Katherine Morgan

Hey, there! I'm Katherine from Northwest Florida. An aquarium specialist, I've kept tanks for over two decades, enjoy experimenting with low-tech planted setups and an avid South American cichlid enthusiast.

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