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How to Prepare Lava Rock for Aquarium: Simple Guide and Tips

Lava rock is one of the best types of rock you can safely put into your aquarium. It is light, looks great, and can support much more bacterial life compared to regular rocks. Their uneven shapes and surface make them ideal for stacking and creating captivating hardscapes.

But even though most hobbyists acquire volcanic rocks from the fish store (as opposed to trekking to a volcanic region and picking them up), lava rocks must be prepared properly before adding them to your fish tank.

The process of preparing lava rock for aquarium with living creatures is relatively straightforward:

  • Wash it under running water with a brush or another scrub
  • Soak the lava rock in water
  • Boil it
  • If the lava rock you got is particularly dirty, soak it in water with vinegar to loosen up the dirt

Let’s go through the steps.

Lava Rock Preparation for Fish Tanks

Making lava rock safe for your underwater pets is relatively straightforward. Driftwood, for example, sometimes needs to be waterlogged, but a few hours of soaking can certainly clean your lava rock.

Equipment you will need to clean lava rock:

  • Bucket or another large container
  • Water
  • Brush
  • Cooking pot (optional)
  • Vinegar (optional)
  • Salt (optional)
  • Hydrogen peroxide (optional)

Whichever method you use, before putting the lava rock into your fish tank, dry it well. It can be dried under the sun, under the AC unit, or in the oven, at a low temperature.

Here are the easiest ways to clean lava rock and disinfect it properly.

Washing Lave Rock Under Running Water

If you have a single large lava rock piece (or two) that isn’t too dirty, you can simply rinse it under running water. Since the aquarium lava rocks are porous and uneven, using a brush or another scrub helps clean the crevices.

Use gloves to avoid cuts on your skin from gripping the rock too tightly and go hard with the brush. Scrub everywhere and use the running water to dislodge and wash away dirt and other debris.

This method could be too time-consuming for an entire bag of small lava rocks, though. You can certainly wash them one by one, but it is easier to use a bucket for the purpose.

Fill up the bucket with the stones and pour in water. Rinse the rocks with your hand, throw the dirty water, and repeat. Do this several times until the water runs clean.

If you’ve bought your rocks from the hardware store or from the barbecue supplies, they will probably be dustier than those sold in pet stores. On the other hand, they’ll likely be much cheaper. Either way, wash the rocks thoroughly before adding them to your tank or you will have to deal with cloudy, murky water.

Soaking Lava Rock

In case the lava rock you’ve procured is very dirty or you wish to save yourself some hands-on time, soaking it for a few hours in warm water will help massively. Just like soaking sticky dishes overnight, water will loosen up the dirt, making active cleaning easier.

Changing the water a few times also helps.

Soaking is very similar to direct washing — you will need a bucket to hold your rocks underwater for a few hours. I prefer to soak my rocks overnight and then give them a thorough rinse.

After that, they go on the stove.

Boiling Lava Rock

Boiling rocks is probably the easiest way to disinfect them. It helps with removing debris, too.

Put your lava rock in a large enough pot so that it’s fully submerged and let it boil for 30 minutes. Nothing complicated there.

Again, let it dry well before adding it to the tank.

Disinfecting Lava Rock with Vinegar, Salt, and Hydrogen Peroxide

You can use salt, white vinegar, and/or hydrogen peroxide to fully disinfect lava rock. Either of these substances works fine, but you can certainly combine them.

If you have a large amount of rocks that don’t fit in a cooking pot, you can dump them in a large plastic container. Cover them with water and add either of the substances. 

In my experience, white vinegar and hydrogen peroxide are a powerful combo that will kill every little living thing on and among the rocks.

Using vinegar and salt also works well to wipe out algae or bacterial life.

As mentioned, this approach is perfect for a large amount of stones. It is ideal for cleaning lava rocks that have been on active aquarium duty, too. If they are changing fish tanks or their current aquarium is undergoing a revamp, giving them a thorough chemical treatment ensures a safe, clean start.

Submerge the rocks in water, add salt, vinegar, or peroxide, and let them stay overnight. A cup of vinegar or peroxide is sufficient for a 25-gallon/100-liter container.

The next day make sure to wash the rocks really well under running water to remove traces of the chemicals. Low amounts won’t harm your fish but do your best to remove everything.

Dry the lava rocks completely before adding them to the fish tank.

How to Choose Safe Lava Rock

Stones are not made equal. Some are better for aquariums than others, and that’s true for lava rocks, too.

Before introducing lava rocks or any other kinds of stone, inspect them. It doesn’t take long and can make a difference in a fish’s life.

  • Make sure the rocks are not too pointy — Lava rocks tend to have sharpish contours. Press your palms against their surface to feel how much their protrusions can cut into skin or fast-swimming medium fish. It’s not a perfect test but touch serves better than sight in this case.
  • Make sure there are no large cracks — Cracked rocks or stones are hazardous. When they finally break, their splits can knock down other hardscape elements or damage plant stems and leaves. Fish or shrimp should dodge the sinking stone easily, but it could hit a particularly unlucky snail.
  • Make sure you like the color — Hardscape color plays a central role in how your aquarium and your fish look. Rocks, background, and substrate can affect fish color quite directly. Generally, a darker substrate makes the fish colors stand out. Black lava rock may have a more striking visual impact, but it is also harder to find and costs more than regular grey-brownish red lava rock.

Making Lava Rock Safe Is Quick and Easy

Follow a basic washing protocol to clean your lava rock and make it safe for fish. If needed, a more stringent chemical disinfection can be conducted, too. If you are cleaning lava rock that’s coming straight from another fish tank, vinegar, salt, and hydrogen peroxide can sterilize anything (including plants).

Simple boiling is efficient by itself and is essential in killing off unwanted pests and cleaning. Boiling water can loosen up a lot of lodged waste and debris.

Boiling, chemical treatments, and scrubbing can make old lava rock look as good as new, removing algae and other superficial discolorations caused by water.

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