How to Clean Rocks for Aquarium Use?

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Aquariums take on a different charm when it’s covered with beautiful stones and rocks at the bottom. However, many fish tank owners know how costly installing these can be. 

If you are the DIY kind of person, you can handpick your rocks and gravel to use. But please do remember that this also carries a risk. 

For one, the rocks could adversely affect the aquarium’s hardness and pH levels that could potentially harm your fishes. Two, it could also bring forth contaminants and other bacteria. 

If you are wondering how to clean rocks for aquarium use, this article can help you out. 

Why should I add rocks to my aquarium? 

There are several advantages you can gain by adding rocks to your fish tank. Aside from enhancing your fish tank’s aesthetic, here are some benefits: 

  • Rocks and stones provide shelter and breeding places for your fish. 
  • You can easily recreate the fishes’ natural habitat using the rocks and stones you have gathered. These then help reduce the stress your fishes are feeling. 
  • Algae also naturally grow on these rocks, providing alternative food sources for your fishes. 
  • Some rock types also help enhance the aquarium’s environment. For example, limestone can increase your tank’s pH levels and serve as a buffer. 
  • Some types of bacteria also grow and colonize on these rocks. These bacteria are vital as they can help eradicate and prevent ammonia, nitrites, and other toxic substances. 

What are some of the disadvantages? 

  • You might have some difficulties cleaning your fish tank as the rocks can trap some food and other debris. You’ll need to remove these decorations to clean your tank thoroughly. 
  • You might also find it difficult to catch your fish or remove dead ones as fishes like to hide in rocks. 
  • Rocks might also contain some bacteria or heavy metals that are harmful to your tank.  

How to Choose Rocks? 

While you can save money by choosing your rocks and gravel to add to your aquarium, you cannot just add any kind of stone. Otherwise, you might have some problems. 

The principal danger of adding handpicked rocks and stones is that they might contain calcium and other hard metals. These substances can significantly alter your aquarium’s pH and hardness levels, making it fatal for your fish tank inhabitants. 

You can test the rock for calcium by adding a few drops of vinegar onto the stone. If the liquid fizzes or foams, then the rock has calcium in it. You should choose another rock or stone in its place. 

Another way to check calcium content is to submerge your gathered stones in the water from your aquarium. First, you have to test them for their pH and hardness levels. 

After, let the rocks and stones sit for a week and then test them again. If you see any significant changes, then it might potentially harm your fish tank. 

Another danger is when the rocks contain bacteria, contaminants, and other organisms that can harm your fishes. 

It’s best to avoid picking rocks coming from highly polluted areas and those coming from lakes, ponds, streams, and other bodies of water. While you can clean the stones, the risk is too significant for your aquarium. 

Moreover, avoid rocks that easily crumble since they tend to be messy. To test this:

  1. Wash the stone and brush it thoroughly.
  2. After, soak it in water for about 24 hours.
  3. When you’re done, brush the rock again and check if pieces are coming off. If a significant quantity is falling off, then it’s likely to degrade in your aquarium. 

aquarium rocks2


What are some rocks to avoid? 

Your fish tank should have a neutral pH and water hardness levels to make it a safe environment for your fish and other aquatic inhabitants. As such, you must avoid rocks that raise or disturb these levels. 

First, you should avoid using carbonate rocks. One of the most common variants you can find is limestone. Adding this is okay for fish tanks with pH levels of 7 or lower, but it can adversely affect your aquarium if it has soft, acidic water. 

Other carbonate rocks include: 

  • Alabaster 
  • Dolomite 
  • Marble 
  • Some types of sand and sandstone 

These rocks are also found to affect your tank’s pH and water hardness levels: 

  • Crushed seashells 
  • Petrified coral 
  • Texas Holey Rock 

What are some safe types of rock to use? 

Here are some rocks you can safely add and use in your aquarium. They can be found in most locations and are also easy to identify. 

These are: 

  • Granite 
  • Lace rock 
  • Lava rock 
  • Onyx and ground glass 
  • Petrified wood 
  • Sandstone 
  • Slate 
  • Quartz 

However, do consider the type and species of your fish. While it might be safe to add into the tank, some of your fishes might not appreciate these rock types. 

Where to find these rocks? 

You can find most of your rocks, stones, and gravel in the great outdoors. Beaches and lakefronts, dry wash beds, and the like are great hotspots. However, most fish tank owners recommend not using rocks gathered from bodies of water, considering the risks. But it’s still up to you. 

If you want, you can also opt to purchase your rocks and stones from garden centers and nurseries, hardware stores, home improvement centers, landscape companies, pet shops, and other similar stores. 

How to prepare the rocks for aquarium use? 

Now that you have gathered enough rocks, stones, gravel, and whatnot with you, it’s time you prepare them for your aquarium. 

Before anything else, make sure you clean the rocks. Thoroughly scrub them with a stiff brush and rinse with clean water. Once you have removed all the dirt and grime, you then proceed to disinfect them. Here are two ways you can do this: 

Method #1: Boil the rocks 

This is the most common and preferred disinfecting method among fish tank owners. 

First, you need to place all your gathered rocks and stones in a large pot and fully submerge them in water. Set it in the lowest temperature setting and cover it with a lid once it starts to boil. 

Leave the pot to boil for about 20-30 minutes. Once it’s done, remove the rocks from the pot. Place them on paper towels to remove excess water and leave it there to cool for at least an hour. You can safely place them in your aquarium once they’re cool. 

This method is not recommended on porous rocks as they will crumble and break apart due to the high temperatures. 

Moreover, be careful not to let the rocks boil for too long. Otherwise, the stones can explode and cause injuries and other damages. 

Method #2: Use a bleach solution 

This method is recommended when you have porous or too-large rocks on hand. 

First, locate a container big enough to place your rocks in. Then, fill it up with water until all the stones are fully submerged. The ratio should be 10 to 1 water to bleach solution; however, others use a slightly higher concentration. 

Allow the rocks to sit in this solution for at least 24 hours. Once the time is up, rinse the stones with water and then let them sit in a bucket of treated water to remove the traces of bleach solution thoroughly. 

Regardless of what disinfecting method you have used, make sure that you test the rocks once again before placing them in your aquarium. 

Soak them in a bucket of water for at least 24 hours after disinfecting. Then, test the water’s pH and hardness level to ensure that it won’t harm your aquarium habitat. 

aquarium (2)



How to decorate your aquarium using rocks? 

One of the most effective ways to spruce up your aquarium is by adding rocks, stones, and gravel as decorative pieces. However, it needs skill and an eye for beauty to know where to place them artfully. 

When choosing rocks and other natural pieces, make sure that they are of different sizes and textures to add depth to your aquarium. Select one of the large pieces to be your centerpiece and use the other smaller rocks as supplementary decorations. If you want, you can also add fake aquatic plants to make it look more vibrant. 

Avoid piling your rocks against the aquarium’s glass, as this can lead to cracks. Moreover, it’s essential to secure your rock piles together. Otherwise, your stacks will easily tumble down due to movements. Some fish tank owners use aquarium silicone to glue their rock pieces together. 


Adding rocks, stones, and gravel into your aquarium certainly livens it up. However, installations can get expensive. 

Nevertheless, you can opt to handpick the rocks and stones by yourself. But it’s crucial that you thoroughly rinse, clean, and disinfect them before you add them into your aquarium. 

Rocks, especially those from bodies of water, tend to be wrought with heavy metals, bacteria, and other contaminants that can potentially harm your tank’s inhabitants.  

Luckily, there are ways you can do this. If you always wanted to know how to clean rocks for aquarium use, hopefully, this article has answered some of your questions. 


Rita Wagener
Rita is a resident paw expert at Pet Keepers. A registered & licensed dog trainer, she also has a degree in animal nutrition, and runs her own dog training course.

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