Can I Use Outdoor Gravel or Rocks in an Aquarium


Can I use outdoor gravel rocks in an aquarium?Decorating your aquarium can give you a liberating feeling. This entails giving your aquarium tons of decorative rocks that mimic the actual seabed. It is reasonable to wonder how can I use outdoor gravel or rocks in an aquarium. But it is also pertinent to know if these rocks are healthy for your aquatic pets.

Adding beautiful rocks inside your aquarium can alter the pH level of the water inside. It can also be a foundation for your fish to have healthy diet as they nimble off the algae on the rocks. It can also nitrify bacteria inside the tank. But first, find out what rocks can provide all these benefits for your aquarium and how you can safely incorporate them in aquascaping.

How to test rocks for an aquarium?

Using outdoor gravel or rocks for your aquarium is safe as long as you know the composition of the rocks that you have. Testing the rocks for calcium content is vital because it can alter the pH of the water and can potentially harm the fish and plants inside.

Testing out the rocks for calcium is easy. Clean the rocks with water to remove the sediments and contaminants first. Next, place a few drops of the common white vinegar on your rock. Foaming of the rock on the surface signifies that it has a high calcium content and can affect the pH and hardness of your aquarium water.

Another way of testing is by placing your set of rocks inside a bucket of water. Take the pH, nitrate, phosphate and hardness of the water with the rocks inside. Leave it for a week and take the measurements again. If you have the same results after, it is most likely safe and will not alter your tank’s water.

Rocks to Avoid, Rocks to Use

In general, it is best to avoid rocks that alter the pH of the water inside the aquarium. Placing the wrong rocks can do more harm than good for the ones living inside.

Avoid rocks that are sharp and those that have holes and pores inside. This is dangerous for fast swimmers because they might not be able to check for the sharpness. You may round off the sharp edges before using them.

Avoid rocks that are high in calcium because they alter the hardness and pH levels inside the aquarium. These rocks include:

  • Limestones
  • Marbles
  • Dolomites
  • Shells and crushed corals

Safe rocks to use include lava rocks, which are known to enrich aquatic plants; slate rocks which are popular as they age well in aquariums; and granite which are safe but can be heavy inside. Other safe aquarium rocks include:

  • Quartz
  • Sandstone
  • Onyx

Where to find rocks for the aquarium?

One of the best things in aquascaping is that the rocks for freshwater aquarium aren’t hard to find. The great outdoors has the best potential for the best suitable rocks. It is free and you don’t disturb the habitat of some animals as you will only need a few rocks.

You can also find the best rocks in lakefronts, riverbanks, along dry wash beds, and more. You should avoid disturbing protected environments like the deep sea, and in places where birds have nested.

Purchasing your own rocks is also an option. You can try going to landscaping and specialized aquascaping stores for specific rocks. Gardens and nurseries will also provide you with a lot of options. Home improvement centers and online shops are also a places where you can shop for aquarium rocks.

Frequently Asked Questions


How long should I boil rocks for the aquarium?

Outdoor gravel and rocks can be home to potential pathogens. Cleaning them thoroughly is an important step before you place them in the tank. Boiling the rocks for 10-20 minutes in tap water can kill these pathogens.

After boiling the rocks, they can remain very hot for some time. Let them sit and cool down before arranging them as you like inside the aquarium.

How to clean river rock for an aquarium?

River rocks look natural and add a pleasing ambiance in you aquarium. They are free and are easy to find. But these rocks are also home to some of the harmful bacteria that can be dangerous to your fish.

Here are simple steps you can do at home to clean river rocks.

  1. Scrub off the rocks with antibacterial soap and warm water.
  2. Rinse with plain water and soak with non-ionized salt water overnight.
  3. Remove the soaked rocks and rinse with water.
  4. Using a bleach solution (1 part bleach, 10 parts water), let the rocks sit for 30 minutes. Rinse with water after.
  5. Take out the rocks and place in an aluminium foil and non-coated pot.
  6. Fill the pot with water and let it boil for 30 minutes to take off the residue.
  7. Rinse it with water and let it soak it again with tap water for 24 hours.
  8. Take out the rocks and place it inside the aquarium

Is aquarium rock safe for fishes?

Aquarium rocks are safe for fishes. These beautiful rocks adds an extra place for them to lounge and eat. It is also a home of good bacteria and algae that your fish can eat off. These rocks are hideouts as fishes play along, a sanctuary for eggs, and a home for invertebrates like corals.


Aquarium rocks add a sense of depth inside a fish tank. It elevates the ambiance of the aquarium, making it a very livable place for your fishes. You will no longer fret on the idea of can I use outdoor gravel or rocks in an aquarium because the answer is a big yes.

There are a lot of benefits of having these unique and gorgeous rocks inside. While they add beauty, it is important to keep in mind the right rocks to use, and the steps in cleaning them before beautifying your aquarium. Rocks give a personal touch to the synthetic place making it homier for your aquatic pets.

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