Rock types you can put in your Aquarium (2022)

Can You Put Rocks from the Beach in an Aquarium?

When it comes to decorating an aquarium, many fish owners want to go the natural route rather than purchase fake items to place in their tank. You tend to find this leads to living plants, wood, and, in many cases, rocks. However, this leads to a question because one common area people find interesting rock shapes is close to the ocean.

So, “can you put rocks from the beach in an aquarium?” Finding rocks on the beach can save a considerable amount of money, yet not every kind of rock type is suitable for adding directly to an aquarium. You should never add rock directly without preparation because they can contain bacteria, or they can alter the pH levels in your tank. Some types of rocks can also include various metals, and these can be lethal for your fish.

Here, you can learn which rock types are suitable for adding to your tank, and how you need to prepare them before placing them with your fish.

Testing Rocks for Aquarium Use

One of the most significant issues with adding any rock to your tank is if it contains any calcium. Any level of calcium can affect pH levels in your tank. To make sure there are no traces, you will need to test them. Here are two ways you can check if the rock will affect your pH levels.

  1. Wash and brush rocks to remove loose grit and possible contaminants
  2. Add a few drops of vinegar or hydrochloric acid (more reliable results)
  3. If there are signs of bubbling, fizzing, or foaming, the rock contains calcium, so don’t use it

The second method takes a bit longer.

  1. Wash and clean your rock
  2. Add some of your tank water to a bucket
  3. Test the water pH in the bucket and write down the reading
  4. Sit the rock in the water and make sure it is fully submerged
  5. Let it sit for one week and then test the pH level
  6. If there is a significant increase in pH, don’t use the rock

Rock Types You Should Avoid

Any carbonate rock type can affect your pH and water hardness. For most fish, this can be harmful, although the inclusion of these can be ideal for African Cichlids. You can use the rock to raise the hardness and pH to cater for cichlids without using chemicals.

Rocks to avoid are as follows:

  • Alabaster
  • Dolomite
  • Limestone
  • Marble
  • Some kinds of Sandstone and Sand

Coral and crushed shells are often in use as substrates and additional decoration; however, these also affect water hardness and the pH level.

Rock Types You Should Avoid

Rock Types Safe to Use in Aquariums

The following rock types are safe to use in aquariums, although they do need to go through the same process of preparation to make sure there are no traces of bacteria.

Granite: Granite is a common type of bright, eruptive rock whose texture is grainy and fanciful. The main composition is mainly quartz and feldspar. It can also contain small amounts of amphibole and mica, as well as other minerals. The primary colors you can find are reds, pink, grays, or whites.

Lava Rock: You can find over 700 types of lava rock, so finding these by the beach can be highly likely depending on where you are. Lava Rock forms when volcanic lava cools. If you see these in the pet store, you can see different colors, yet they are mostly black or gray, yet the more popular colors are a mix of red and orange.

Lava rocks come with a high pore count, although they are durable and long lasting. They may require pre-treatment, but when placed in a tank, they are ideal for the growth of healthy bacteria.

Onyx: Onyx is a gemstone that consists of silica, quartz, and moganite. These minerals make up the chalcedony stripes inside the stone. You can find these vary in color from white to almost any other color variation. You may find conventional onyx formulations containing streaks of black or white.

Quartz: Quartz is a mineral with a main component of silicon. It is a translucent and attractive looking crystal gem, which has the appearance of a diamond. You can find it in a variety of colors like purple, yellow, pink, black, or white. It won’t alter the water parameters, so it is a safe aquarium rock suitable for any fish tank.

Under quartz, you can add Petrified Wood. You now see these as remains of wood. All the organic remains are now fossilized, and replaced with quartz chalcedony minerals.

Slate: Slate is a fine-grained metamorphic rock consisting mainly of volcanic ash, clay, and quartz. There are many kinds of different colors, such as gray, purple-green, and cyan-blue. Slate is extremely durable, so it will last a long time and is ideal for the water landscape in your tanks.

How to Prepare Rocks for Aquarium Use

Once you have chosen your rocks and tested them to see if they contain any calcium, and they are suitable for your tank conditions, it’s time to start preparing so you can use them. If you haven’t done so already, it will be time to clean them thoroughly. Using fresh, clean water only, you should clean them off with a stiff brush.

It may be tempting to use a household cleaner, yet refrain from this as they can leave residue on or in rock crevices that can harm your fish. Once clean from all traces of dirt and grime, you can then select either of the two methods here to disinfect your rocks ready for use.

How to Prepare Rocks for Aquarium Use

Boiling Rocks for Aquarium Use

While this is the preferred method of sterilization, you can find some hazards when you begin boiling rocks. You should never allow them to boil for extended periods or leave them unattended as they can explode if they become too hot.

It is advisable to wear personal safety equipment while boiling rocks on the off chance one decides to explode and fragment. The safest way of boiling rocks is by placing them inside a large pot where you can fully submerge them.

Bring the water to a simmering boil on the lowest heat where you can maintain this. You also need to make sure you cover the pot as the rocks are simmering.

Boil for between 20 to 30 minutes and remove from the heat to cool. Once cool, you can remove them from the pot where you can place them on a drainer of paper towels for the excess water to drain. When they are dry, you can then add them to your aquarium.

Note: While this works for the majority of rock types, it isn’t suitable for rocks that are porous such as Lava Rock, as they can break apart during boiling.

Soaking Rocks in Bleach for Tank Use

Where the above methods are suitable for non-porous rocks, this means of sterilization is preferable for porous rock, although it is not as effective as boiling. You can use this method for rocks that are too large, and you can’t place them in a pot on the stove. Any large plastic container is suitable where you can fully submerge your chosen rocks.

Once you sit your rock in the water, you need to use one part of bleach to ten parts of water (10:1). You will find this equates to one-half gallon of bleach to five gallons of water if you can submerge your rock in less water.

Soaking Rocks in Bleach for Tank Use

It is possible to use a higher concentration of bleach, although this takes more rinsing. Let the rock sit under the bleach water solution for twenty-four hours. Remove the rock and rinse thoroughly (once or twice) with fresh, clean water, or rinse under the tap.

Some tank owners dip their rocks in treated water to be sure no bleach traces are remaining.

It is worth noting that after 24-hours in sunlight, chlorine in bleach breaks down and isn’t effective. If you think more than twenty-four hours soaking will do better, you will find you are wasting time. You can also find this is one method used for cleaning air-stones in your aquarium.


As long as you choose rocks, which won’t affect the conditions of your tank water, it is safe to use any of the above, after following the sterilization process.

The only other things you have to be cautious of are there are no sharp edges to your rocks and line the inside of your tank where your rocks will be sitting. Direct contact between your tank glass and acrylic bottom needs avoiding at all times.

Before you begin sculpting your aquascape, you do need to consider the weight of your rock and the weight of your water once you start filling your tank. The weight can considerably increase once you add the weight of both together.

Once you tend to all the requirements, you will find a rock can be a fantastic addition to your tank, and it looks nice as well as giving your fish places to swim and hide.