The best aquarium rock not only helps you decorate your tank but acts as a playhouse for your fish. But selecting suitable rocks for your aquariums can be challenging as some rocks also affect the pH level of the water.

To help you out, we have handpicked the best aquarium rocks that you will buy in 2021.

And to help you pick the right one, we also have a comprehensive guide that will help you make the right buying decision at the end of this article.

So let’s get started.

Comparison Chart

Products Weight Rock Type Nature
Pisces 17 pounds Metamorphic Increases pH
Natural Slate

5 pounds Metamorphic and sedimentary mix  pH neutral

20 pounds Metamorphic pH neutral

5-20 pounds Sedimentary  pH neutral

The Best Aquarium Rocks

1. Pisces 17lb Seiryu Rock


  • Do not discolor water
  • Boosts algae growth
  • Mimics the natural habitat of fishes
  • Decreases nitrate and ammonia levels of water
  • Comes in various sizes


  • Slightly heavy

Seiryu rocks are the most popular choice among aquarists to decorate their fish tanks and for excellent reasons. These rocks are extremely beautiful, strong, and easy to clean. However, finding these rocks is not very easy.

So to keep up with the demand, most Seiryu rock sellers in the market actually deliver Ryuoh stones, a cheaper but much less colorful alternative of Seiryu stones. Pisces, on the other hand, provides genuine Seiryu stones of adequate sizes.

The package includes a large rock, two medium-sized rocks, and three to four small-sized rocks, which are enough to decorate your entire aquarium.

These Seiryu stones are of blue and greyish color and have a slightly lighter contrast, making them a perfect match for aquariums with green plants. Another amazing quality of Seiryu rocks is that they have edges and cuts where your fishes can hide and play.

The large rock is big enough to become the center of attraction of your aquarium, and the smaller-sized rocks fill up the remaining void. Pisces manually handpicks the best rocks that they include in their package.

They choose these rocks based on shape, size, color, and, most importantly, quality. So you can be assured that the rocks you will receive will not just be small broken pieces.

Adding too many Seiryu rocks can increase the pH levels of the water, so you need to moderate the number of rocks you use in your aquarium. However, you can always balance the pH level by adding some driftwood.


This Seiryu rock from Pisces is perfect for aquariums of all sizes. It is nontoxic and gives a luxurious appeal to your tank. To create the best ambiance, add some lights and watch the rocks glow as they reflect the light thrown on them.

2. Natural Slate Stone


  • No alliteration to water chemistry
  • 100 percent natural
  • Best for spawning and feeding
  • Heat retention properties


  • Sharp edges

Slate is primarily a metamorphic rock mixed with several sedimentary rock materials. It is found on the underground surface of the earth. It is dark grey in color and is one of the best decorative rocks for aquariums. This natural slate rock collection weighs 5 pounds and comes with a mix of stones that range from 3 to 5 inches in size.

Since it has such a narrow structure, it can be used in many exciting ways. You can use it as a standalone piece and also along with other wooden pieces or stones.

As they can be piled above one another, it acts as a great building material to construct caves or different structures. It is lightweight and usually small in size. Additionally, they have a smooth surface which makes it excellent for fishes to lay eggs on them.

Even though the slate rock is usually safe for freshwater aquarium use, it is advisable to perform an alkaline test on the rock if you plan to add it to an aquarium that requires strict pH regulation.


Slate stones are great for freshwater aquariums and especially for fishes that need a warmer environment as they retain warmth naturally. So if you are looking for natural aquarium stones that are easy to maintain and durable, this is a great option to consider.

3. CURRENT USA Seiryu Stone Collection


  • Porous structure
  • Shelter for algae and mosses
  • Creates a natural environment
  • Durable
  • Neutralizes nitrogen


  • pH neutral

This Seiryu rock collection from the CURRENT USA is one of the best large aquarium rocks available in the market. Even though just like the Pisces Seriyu rocks, It falls under the same metamorphic family, they are slightly different from each other.

These rocks are heavier and also have a higher density as compared to other Seiryu rocks.

You will find 7-11 pieces of dark greyish-colored Seiryu rocks of different sizes in this package. These rocks are also more significant than the Pisces Seriyu rocks, which make them suitable for tanks of up to 48 inches.

Another great quality about these rocks is that they are pre-washed and ready to be put into your aquariums.

They have a porous structure that helps in the growth of bacteria and algae, which lowers the nitrate levels of your tank while also providing food for the fish. Additionally, It has sharp edges and a vivid texture that creates a mountainscape appearance inside the aquariums. The rock’s marine-based sediments qualify it as one of the best aquarium rocks for freshwater aquariums.

If you are setting up a freshwater water tank for a cichlid, then Seiryu stone is the most suitable option for you. This is because these rocks are big enough for cichlid to play around and hide, making them feel comfortable and relaxed. However, these rocks are also safe for shrimps like Amano shrimp, red cherry shrimp, and glass shrimp.


If you are looking for large aquarium rocks for your aquarium that are not only pH neutral but also durable, then the Seiiryu stone collection from the CURRENT USA is the best choice for you. Unlike other stones, it has a higher density which makes it add to its durability. Since it does not break or leach, it also does not alter the pH level of the water.

4. Aqualexs Aquarium Ohko Dragon Stone Rock


  • Suitable for pH-sensitive fish and plants
  • Lightweight
  • Good for shelter
  • Inexpensive
  • Natural tan color


  • Brittle in nature

Dragon stone is known for its unique colors and dramatic effects on aquascapes. Its stunning structure and subtle earthly tones provide instant warmth and a natural aesthetic to your aquarium. It is highly porous and has a very uneven design with cave-like projections that creates space for small fish to find shelter.

Nature worked hard on this rock and shaped some decent features. The origin of the Ohko stone is a result of the tide, sun rays, and climate change that helped in adding remarkable attributes to its appearance. It has a scale-like appearance and carries a greenish-brown color due to the mixing of clay and microorganisms.

You can use this rock as the centerfold of your aquarium as it mimics the ocean bed and creates a very natural environment for your fish which makes them feel relaxed. Ohko stone is ideal for both freshwater and saltwater aquariums as it is completely inert and does not alter the pH level of the water. Additionally, it naturally provides minerals for aquatic plants to flourish.

However, there are a few downsides that come with this rock as well. The most significant issue is that this rock can cause water to get cloudy if it’s not cleaned regularly. Additionally, Ohko stone is also very fragile, so you need to be careful while cleaning it, or it may break.


Overall, Ohko stone is a pure gem. It becomes the center of attraction of any tank it is put in and enhances its beauty. Since it does not alter water chemistry, it is safe to use with both saltwater and freshwater tanks. However, make sure to clean these rocks properly before adding them to your tank.

Things to Consider Before Buying Rocks for Your Aquarium

Not all rocks are suitable for all aquarium types. Adding the wrong kind of rock to your aquarium can cause an imbalance to your tank water’s chemical composition, which can harm your fish. You also need to make sure it is of the right size and weight.

Here are a few essential things you need to look for before buying rocks for fish tanks.

– Type of Rocks

The most common types of rocks used in aquariums are metamorphic rocks, sedimentary rocks, and igneous rocks.

Let’s break down each of them to understand which one is best for you.

  • Metamorphic rocks: Metamorphic rocks are formed due to intense changes in temperature or pressure, which makes them the most durable of the bunch. The best example of metamorphic rocks used in an aquarium is slate. These rocks never deteriorate and are very durable. Even though they are neutral in nature, sometimes adding too many of these rocks to any aquarium can slightly alter the pH level of water.
  • Sedimentary rocks: These aquarium-safe rocks are formed by continuous erosion and weathering and accumulation of sediments under extreme temperature and pressure. They are the best rocks for freshwater aquariums as they are entirely pH neutral. However, since they are not very dense, they deteriorate faster than metamorphic and require additional maintenance. Some examples of sedimentary rocks are Ohko Dragon Stone, sandstone, breccia, conglomerate, and shale.
  • Igneous rocks: Igneous rocks are one of the popular choices for aquarium rocks, majorly due to their beautiful glass-like composition. These rocks are formed due to the cooling of magma or lava. They are an ideal choice if you want to go with a particular theme for your aquarium, as they come in various color schemes. The most commonly used igneous rocks are Granite and Basalt. One thing to keep in mind is that some igneous rocks can alter the pH level of water and can also turn out to be acidic in nature. They are also relatively expensive and rare. However, you can always go for artificial aquarium rocks as they look exactly like these igneous rocks.

– Pick to Correct Size

The perfect size of the rocks depends on your aquarium’s capacity and the breed of fish that you have. If the rocks are huge compared to the fishes, they might crawl in the crevices, and if they are too tiny, large fishes can ingest them, which could be extremely harmful.

The size also depends on the purpose of the rocks. If you are using them to line the bottom of the tank, then rocks ranging between 1-4 inches in length are ideal. However, if you are using them for decorations, then you should choose larger rocks.

If you choose to add heavy rocks to your aquarium, make sure your tank can sustain the extra weight. Feel free to use the below-mentioned steps as a checklist to avoid any accidents.

  • Make Sure Your Tank Has Proper Support: It is essential to provide the tank with a flat bottom and a stand that supports the entire base of the tank. Also, make sure that the weight is distributed correctly as some of these stones can become very heavy, and applying too much weight anywhere on the tank can damage it.
  • Create a buffer between the base and the rocks: It is advisable to use styrofoam between the base and rocks to absorb excess pressure and prevent the unequal distribution of weight. This tip will save your tank from getting scratched or chipped due to the sharp edge of some stone. However, if you have an acrylic tank, you can skip this step.

– Safety

Fishes are generally sensitive to changes in the pH level or temperature of the water. Therefore it is essential only to use those rocks that are compatible with your fish. However, irrespective of the type of water, all rocks should be nontoxic and should not have any sharp edges that can injure the fish.

It is also essential to wash the rocks before adding them to your tank, as they might have packaging residue or dust on them. This step can alter the pH and hence prove harmful for the fish.

A quick way to find out whether the rocks are of the correct pH level or not is to add a few drops of acid on top of the rocks. If it fizzes or forms bubbles, it means that the rock can severely increase the pH level of the water.

– Maintaining and Cleaning Your Aquarium Rocks

The only sad part about owning a fish tank is cleaning it, and the selection of your aquarium rocks can have a significant impact on the time taken to do so. Aquarium rocks tend to build up a lot of residue and dirt on their surface, which needs to be cleaned regularly. It is advisable to clean your tanks once a week, but a thorough cleaning is required at least once a month.

It’s always better to use low-maintenance rocks like slate, as they last for a very long time and don’t break by applying slight pressure. This makes them easy to handle and clean. It is also important to note that porous rocks like the Ohko Dragon stone can be tough to clean sometimes as it breaks very easily and constantly deteriorates.

Unfortunately, just adding a water filter won’t be enough as the dirt can accumulate between the cracks and pores of the rocks, which can only be cleaned with a brush.
Follow these steps to efficiently clean your aquarium rocks.

First, fill up a bucket with some clean, fresh water and soak the rocks in it for 60 to 90 minutes. You can also add a cleaning solution to this bucket. After the rocks are soaked properly, use a sponge to individually clean each one and keep them in a separate bucket filled with fresh water.

Make sure to clean every crack, crevice, and pore and remove all the surface buildup. The next step is to rinse the rocks under running water and put them out to dry. Make sure you only add the rocks back once they are completely dry.


There are a lot of rocks that look very similar to each other but have entirely different properties. Getting the wrong rocks can negatively impact your tank’s water chemistry, which can be very dangerous for your fish.

To avoid such situations, make sure to only buy aquarium rocks from reputable sellers like the one we have mentioned on our list. However, if you are not sure which rock to go with, then we suggest you go with the Aqualexs Ohko Dragon stone as it does not alter the pH level of your water. It is also lightweight and comes in all sizes ranging from 1 to 10 inches.

It has a beautiful color that gives a very natural appeal to your tank while also comforting your fish.

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