Can You Use Lava Rocks in A Fish Tank—Are They Aquarium Safe

Can You Use Lava Rocks in A Fish Tank—Are They Aquarium Safe

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I’ve heard a lot of questions on the use of lava rocks in fish tanks, including where to get the best lava rocks. But most fish keepers just want to know if these rocks are aquarium safe, and if so, how to prepare them for aquarium use.

Well, you came to the right place if you’ve had any of these questions because, in this article, I plan to talk everything lava rocks.

To begin with, are lava rocks aquarium safe, can you use them in your fish tank?

Yes, for the most part, lava rocks are aquarium safe and are especially useful when keeping cichlids. Apart from making good fish tank decor, they are porous hence grow beneficial bacteria that aid in filtration.

The healthy bacteria that grow on lava rocks will remove nitrates in your tank and improve your water quality.

Please read on for more insight on the use of lava rocks in freshwater fish tanks including for filtration, substrate, and more.

Lava Rocks For Aquarium Filter

As I had mentioned, lava rocks are porous hence perfect for providing the ideal living environment for beneficial nitrifying bacteria. These bacteria are crucial in all fish tank environments as they are responsible for breaking down excess nitrates, and expelling them from the water column.

How these works is water sips into the lava rocks through tiny holes on the surface, then the bacteria housed inside the rocks consume oxygen in the water creating an aerobic environment.

In this aerobic environment, the denitrifying bacteria then consume nitrates to produce oxygen and nitrogen, thus removing any excess nitrates from your water column.

This will go a long way especially if you are struggling to keep your the levels below the recommended 20ppm, and do not have plants to consume the nitrates.

Moreover, you can use lava rocks as filter media in your biological filter unit.

If you are tired of spending tones of money on biological filter media, lava rocks are a dirt-cheap alternative. You will get large bags of these rocks in your local hardware store, sometimes for as little as five dollars.

When looking for lava rocks, please note that you may not get them n the aquarium or pet section, instead, visit the barbeque-grill section or lawn and gardens before you give up.

Once you have your rocks, all you need to do is clean, prepare, and pack them in your filter and they’ll clean your water as any filter media would.

How To Clean, Prepare Lava Rocks For Aquarium Use

Preping lava rocks for aquarium use is pretty easy and somewhat straight forward. It’s exactly like washing your substrate before adding it into your fish tank.

I just put my rocks in a bucket (5 gallons) and then run cycles of hot water through the rocks.

A majority of lava rocks will release a reddish-color into the water, so I keep repeating the cycle until the water runs clear, and that about it.

You may want your rocks to sit in the sun for a day or two before you pack them in your filter or fish tanks. This ensures no residual water or debris from the washing you did gets into your filter unit or aquarium.

Below is a quick 4-step checklist.

  1. Place your lava rocks in a 5-gallon bucket.
  2. Add water in the bucket and using a brush, scrub the rocks to remove any detritus on the surface and crevices.
  3. Run cycles of ht water in the rocks until the water runs clear of any dirt or reddish coloring.
  4. Dry your lava rocks in the sun for a day or two before packing them in your filter or adding them in your tank.

Can You Use Lava Rocks For Aquarium Substrate

Lava rocks substrate would be great for beneficial bacteria, but the rocks are better suited for use as biological filter material inside your aquarium filter or as part of your hardscape.

Another common use of lava rocks in aquariums is as a substrate, and YES, its perfectly ok, so no need to worry.

When crushed, the lava rocks will create a pretty decent base for your tank as well as an aerobic environment for beneficial bacteria to thrive.

Because lava rocks are inert, the substrate will rarely cause changes in your water parameter, albeit some fish keepers believe the rocks do release undesirable gases and trace metals from their structure into the water.

Lava rocks can even be used as a substrate in planted aquariums because they provide great water movement. But remember to place root tabs in the substrate for your plants because these rocks, as I said, are inert.

Under the substrate, use lava rocks to bulk up your aqua soil as an alternative to power-sand or to substitute aqua-soil when you need to create a slope inside your fish tank.

This is especially helpful because both aqua-soil and power-sand are quite costly, while lava rocks are dirt-cheap, meaning they will help lower the amount you’ll need, and the cost you incur.

The only thing to note should you decide to use lava rocks as an alternative to aqua-soil or power-sand is the lesser mineral content in the rocks.

For perspective if I may: Aquasoil is the recommended substrate for planted aquariums, it provides the best media for roots to thrive while contributing essential nutrients for plants development and regulating the ph to an ideal level.

Whereas, power-sand is base substrate material designed to provide nutrients to the roots of aquatic plants and promote growth. Power volcanic stones also secure the water circulation and organic nutrients for plant development.


Away from the use of lava rocks in aquariums filters and substrate, here are two more questions I’ve come across more than once.

Can You Use Red Lava Rock As Aquarium Substrate?

Yes, you can use red lava rocks for your fish tank substrate, just make sure you clean them thoroughly before you placing them in your aquarium.

Ideally, clean any detritus on the rocks’ surface with a brush, then run hot water through them until the water is clear, with no reddish traces.

That said, the red coloration is caused by oxidation of iron, which is not harmful to aquarium fish especially in lesser, inert amounts as in lava rocks.

Do Lava Rocks Affect Aquarium ph?

No, lava rock do not mess with your ph at all and are perfectly fine for the fish you are keeping. The rocks are mostly stable, or inert if you will, so no need to worry.

As for your overall tank health, lava rocks will also not affect your overall water chemistry, if anything, they will help clean your water of excess nitrates, hence perfectly ok for use in your filter and as a substrate.

Eddie Waithaka

Resident Content Creator and Marketer at AquariaWise who talks about aquariums and fish and aquascapes a lot.

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