Aquarium Safe Rocks – What Makes Rocks Aquarium Safe?

Estimated read time 18 min read

In this article, we’ll explore all the many different Aquarium Safe Rocks that you can use in your aquarium.


The Three Different Types Of Aquarium Rocks

Rocks have many properties that can be overwhelming to consider and understand their importance when choosing the suitable rocks for your aquarium. However, you will find that rocks are broadly defined by the following three categories that will help you narrow down your search:


The cooling of molten earth substances forms igneous rocks. While that sounds exotic and hard to find, they’re very common and found in many fish tanks.

Igneous rocks are arguably the most common that you’ll find in aquascapes across the world. Dolerite, gabbro, lava rock, basalt, granite, and many more are frequently used as decoration.


Sedimentary rocks are trickier as they can sometimes dissolve in water. Still, many types of sedimentary rocks find their way into aquariums regardless. Ordinary aquarium sedimentary rocks include breccia, shale, sandstone, marl, and breccia, though there are many more that you can use.


Our third category is metamorphic, which comes from transforming other rock types. Most commonly, this is from heat and pressure causing a change in the rock, resulting in one of many metamorphic rocks. Common metamorphic rocks in aquariums include quartzite, slate, schist, and marble.

Here’s Our List of Aquarium Safe Rocks

You have a significant number of options when it comes to what sort of rocks you want to put into your aquarium. Following is our list of aquarium-safe rocks that you can use for decoration. Each of these will make a great, safe addition to your growing setup.

Seiryu Stone

PINVNBY Aquarium Decorations Natural Seiryu Stone Rock 4.5lbs Mixed Sizes Gorgeous Aquascape PH Neutral Perfect Select Packages Gravel Rock Iwagumi For Aquascaping Aquariums, Reptile & Amphibian Tanks

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Starting off our list is one of the most popular and well-known rocks for aquascape decoration, the Seiryu stone. Many consider this to be the pinnacle of aquatic decoration rocks. Its popularity is so widespread that you would likely struggle to find many aquariums that don’t have Seiryu stone somewhere inside.

Seiryu stone is known to slightly raise pH and water hardness, though not severe. Therefore, if you only intend to add one or two stones, you may not need to alter things at all. However, one of the most known cons is that adding in a good amount of Seiryu can make your water too alkaline.

Still, this off-white stone is amazing for a natural-looking landscape. Moreover, there’s a high chance that you’ll be able to find it easily in local stores due to its popularity.


  • Sturdy
  • Common and easy to find


  • Can alter water pH

Mountain Stone

Natural Slate/Quartz Aquarium Stones - Size 1 to 3 Inch. PH Neutral. Perfect Rocks for Aquascaping Aquariums and Nano Tanks, Reptile and Amphibian Enclosures (5 lbs) (1 to 4 Inches)

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Mountain stone is newer to the aquascaping world but has taken off in popularity considerably. It’s particularly notable for irregular, unique shapes that provide a one-of-a-kind appearance to your aquascape. The jagged form also helps stack them to create artistic impressions in your aquarium.

One of the cons is that it’s highly porous, making cleaning them thoroughly tricky. However, many also view it as a pro since it helps many aquatic mosses or plants attach. Such a quality makes mountain stone highly useful in stacking for decorations.

Another great thing about mountain stone is how light it is due to its low density and high porousness – the low weight helps with stacking and makes it so that there isn’t as much of a risk if it falls.

Don’t let the name fool you, though – mountain stone is a specific type of rock. So don’t walk around in the mountains and think that any stone you pick up is aquarium safe!


  • Easy to stack
  • Great for plants


  • Difficult to clean

River Rocks

Royal Imports 5LBS River Rocks Decorative Ornamental Pebbles, Garden Landscaping Stones, Gravel Filler for Plants, Vases, Succulents, Home Decor, Aquariums, Crafting, Animal Habitat - Large Natural

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As their name suggests, river rocks have spent a certain amount of time in a river. Due to the natural forces, they tend to be very smooth. While these can also be manufactured, they are easy to find in a river.

If you’re getting them from nature, ensure that you’ve cleaned them thoroughly before putting them into your aquarium.

These stones are great for setting groundwork but can leave gaps between them. Many pair them with gravel to fill in those gaps. They aren’t very good for stacking due to their round and irregular shapes.


  • Easy to find
  • Fits any aesthetic


  • Difficult to stack

Petrified Wood

Underwater Treasures Petrified Wood - Large

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Despite the name, petrified wood isn’t wood at all. Instead, it’s a sedimentary rock often referred to as fossil wood or petrified stone. Petrified wood is mainly silicate minerals similar to quartz, calcite, pyrite, and opal.

One of the many benefits is that petrified wood can take nearly any shape, just as wood can grow in plenty of different forms. However, it might have toxic minerals, so make sure you’re getting it from a reputable source. Even then, you should still consider cleaning and sanitizing your petrified wood before using it.

Petrified wood is also highly durable and hardy. In terms of acidity, this stone is neutral, meaning it won’t throw off the balance of your aquarium much. Additionally, it contains a high amount of iron that can benefit the plants in your aquarium. Because of this, it’s extremely useful for aquariums that have a high amount of plant life.


  • Sturdy and flexible
  • It comes in many different shapes


  • Can be toxic

Natural Slate

Natural Slate Stone 3 to 5 inch Rocks for Miniature and Fairy Garden, Aquascaping Aquariums, Reptile enclosures & Model Railroad. (5lbs)

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Natural slate is a flat, layered rock easily found in nature – and most aquascapes. It’s handy for stacking because of its flat appearance. More often than not, slate pieces are larger but not very thick, making them great close to the ground.

Slate is also extremely easy to find, as it’s also a common gardening stone. Most gardening or home improvement stores will sell it at a low price, making it great for starting your aquascape. Just make sure that you clean these stones before putting them into your aquarium!

One con to be aware of is that the edges of the slate can be sharp enough to cut into your hand. Not only is this an obvious hazard to you, but it can also injure or even kill fish in your tank.

Thankfully, slate is easy enough to break that you can smoothen out these edges. Make sure that there are no jagged, sharp pieces to your natural slate before you put them in. Doing so makes maintenance safer and avoids hurting the inhabitants of your tank.


  • Flat, easy to stack
  • Easy to find


  • It can be sharp, dangerous to fish
  • Very fragile, especially if dropped

Dragon Stone

Aqualexs Aquarium Ohko Dragon Stone Rock Mixed Sizes

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Also referred to as Ohko stones, dragon stone is a scaly, all-natural sedimentary rock. However, many believe the stone is artificial due to its appearance. Dragon stone consists of silt, clay, and organic matter packed tightly together by high pressure.

Because of the high amount of clay, dragon stone has a low weight, which, along with its unique appearance, makes it as popular as it is.

One of dragon stone’s appealing characteristics is the many crannies and crevices across the surface. It also resembles petrified wood and driftwood, which is useful for coastal decorations and aesthetics.

Lightweight, natural, and beautiful, dragon stone is one of the most popular choices for a good reason.


  • Unique appearances
  • Lightweight, natural appearance


  • It might be overly porous for some
  • Difficult to clean

Slate and Shale

Natural Slate Stone - 1/8 to 1/4 inch Slate Gravel | Perfect for Basing Models, Aquariums, Bonsai and Miniature Gardens, 1lb

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Slate and shale are often put into aquascapes as a pairing due to their similar appearance and composition. However, natural slate is much wider than shale, whereas shale tends to be smaller, thicker.

Shale also has the same jagged, sharp edges as slate, so use the same precaution you’d use with slate. Otherwise, slate is excellent for filling in the gaps of shale.

It’s excellent for a jagged, otherworldly appearance or a cave aesthetic. Whatever you pick, these rocks go together perfectly for beautiful aquariums.


  • Flat and easy to stack
  • Low cost


  • Fragile
  • It can be sharp, dangerous to fish

Lava Rock

BCQLI 400g Sphere Bio-Filter Media for Marine and Freshwater Aquariums, Red Volcanic Rock

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Lava rock is an irregular, lightweight stone that comes in various colors. Most times, this stone appears reddish to red-brown but comes in black variations as well. As the name suggests, lava is usually created in contact with rocks.

Because of this, it’s often used for islander or Polynesian aesthetics. Pacific or saltwater aesthetics will also commonly use lava rock.

One thing to be aware of is that it’s often highly porous. That makes it common for use as a filtration device for aquascapes that don’t use pumps or filters. Being lightweight also helps beneficial bacteria colonize, and many smaller mosses can use it as an anchor point.


  • Lightweight
  • Porous


  • Difficult to clean


Quartzite is similar in shape and size to natural slate in that it often has a wide, flat appearance. However, the combination of iron oxide, silica, and other natural materials gives it a streaking, shimmering pattern.

Polished quartzite is a common decorating material in many deployments, including countertops and tiles. In an aquascape, quartzite makes for a great addition to soft water tanks. Freshwater aquariums will often use quartzite to this end.


  • Easy to find
  • Fits any aesthetic


  • Fragile



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Granite is one of few stones that won’t affect the pH balance of your aquarium. Also, due to its toughness, granite won’t dissolve like some other rocks or give off any chemicals. It also means the cleaning is much easier and more effective.

However, that toughness comes at a high weight, which is why it can be risky to stack granite rocks; just one of them falling could end up cracking the aquarium’s glass.

Regardless of granite’s placement, its weight can still be strenuous. So make sure you take that into account when deciding on how many of these beautiful rocks you’ll put in your aquarium.


  • Very heavy
  • Sturdy and long-lasting


  • It can be dangerous due to weight


Onyx Sand, 7 kg / 15.4 lbs

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Onyx is inert and, as such, will not affect the pH balance of your aquarium. It’s a gorgeous, layered rock that is useful for any style of aquascape. However, it is somewhat sharp, which can sometimes endanger the fish if you don’t smoothen it out.

Onyx comes in many shapes and sizes, though most prefer it in smaller pieces. It’s commonly used with slate and shale and is effective in cave-like aesthetics.


  • Neutral pH
  • It fits many other rock aesthetics


  • It can be sharp, dangerous to fish

Glass Rock/Pumice

KISEER Clear Aquarium Glass Stone Bulk 1 LB Sea Glass Beads Gems Marbles Pebbles Gravel Rock for Aquarium, Fish Tank, Garden, Vase Fillers, Succulent Plants Decor (Sea Blue)

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Pumice – a type of glass rock – is a form of volcanic glass similar to obsidian. Many refer to pumice as “floating stone” due to its extremely light density, which causes it to float on water. It’s also why pumice can be challenging to use for decoration.

It’s highly porous, making it useful for plants and fish that want somewhere small to hide. However, it’s tough to clean properly, so be careful where you source it from and do your best to ensure its cleanliness yourself!


  • Very light
  • Highly porous


  • Difficult to clean
  • It might be too lightweight!

Texas Holey Rock

Texas Holey Rock Aquarium Decor for Fish and Aquatic Pets to Swim and Hide | 20 lb

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Also called honeycomb limestone, Texas holey rock is popular among aquascape designers. Weathered holes and crannies provide ample areas for fish to hide in. In addition, the rock is typically much larger – enough to be the centerpiece of most aquascapes.

The rock is typically lighter and has a white appearance. If you intend to maintain that white appearance, you will need to clean it consistently, but the discoloration won’t be too severe in most cases. Given enough time to season in a tank, it will hold a beautiful natural color instead.


  • Long-lasting
  • It’s meant to stay in a tank for years
  • Grows character with age


  • Requires high maintenance to maintain white coloration

Rainbow Rock

Rainbow rock has a stunning appearance that lives up to the name, though much of the coloration centers around deep reds and oranges. Moreover, complex layers create beautiful designs that never replicate, making each piece unique.

Rainbow rock is commonly used for canyon or desert appearances. While a desert appearance may sound strange for an aquarium, there are many beautiful designs that you can employ with the right sand. Unique, complex, and gorgeous, rainbow rock makes a fantastic addition without heavily affecting the pH of your aquarium.


  • Extremely colorful
  • Each rock is unique
  • Neutral pH


  • It fits some aesthetics more than others

Plastic Rocks

Lava Rock Formation for Aquariums Or Vivarium's, Artificial Extra Large Ornament, Fish & Aquatic Habitat Safe

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The last aquarium stone to discuss isn’t a stone at all but a facade. Plastic rocks are extremely common, and you’d likely struggle to find a store that doesn’t sell some sort of plastic rocks.

Many enthusiasts worry that putting plastic in their aquarium may have harmful effects, but don’t worry. Plastic rocks of decent quality will not pollute your water – but make sure they aren’t low-quality, as they can have harmful effects!

Plastic rocks are much cheaper than many stones. However, they often fail to have the same natural appearance and can sometimes be difficult to anchor down. It’s also worth mentioning that plastic rocks rarely last as long as natural stones, even when compared to softer rocks.

A primary benefit is that they can fit any shape or size. Plastic rocks can be porous, so plants have anchor points and smaller animals have hiding places. Plastic rocks are great to fulfill a need on a budget without searching for a specific rock.


  • Easy to find
  • Generally cheap
  • It comes in endless varieties and designs


  • It doesn’t last as wrong as real stone
  • Can sometimes pollute water if wrong plastic is used

How and Where to Find Aquarium Safe Rocks?

Finding aquarium-safe rocks is pretty straightforward. Depending on your location, you can find them in nature. However, in that case, you will need to clean and prepare them to make them safe for your aquarium.

The other option is to head to a local pet store, as most sell aquarium stones. Craft and hobbyist stores are a viable alternative as well. If you can’t find what you’re looking for, you can always browse online stores and sellers that will also likely have a wider selection.

Can You Put Normal Rocks in a Fish Tank?

The answer to this depends on how you define “normal rocks.” If you mean outdoor rocks, this is always a gamble. You should identify and clean any rocks before putting them into your aquarium, especially if other living things are already inside the aquascape.

If in doubt, do not place a rock into your aquarium. Adding the wrong material into your aquarium can and will have drastic effects, even causing the death of every living organism in the water. Correctly identifying these rocks is key to ensuring that you have something safe to put into your aquascape.

Are All Rocks Aquarium Safe?

No, not all rocks are aquarium safe. Many rocks can disrupt the water, be too heavy for the tank, or cause other threats. Once a rock is correctly identified, you can research it further to see if it’s safe for your aquascape.

What to Look for When Buying Rocks for Your Aquarium

Make sure that you aren’t sourcing your rocks from an untrustworthy source or someone that you don’t know the record of. If it’s an individual online seller, pay close attention to reviews and other users’ comments to know if the rocks are safe. Some rocks also look similar to others and can lead to a difference in price.

Individual rock characteristics depend on what you prefer. You want something tough enough that it won’t dissolve over time in your water. You also want to make sure that the stone is as close to neutral as possible.

If you intend to keep your aquarium isolated to rocks or non-living decorations, pH balance becomes much less vital. For these decorative styles, anything goes – though you still want to avoid rocks that dissolve easily for longevity’s purpose.

The final thing to look for is entirely personal – a chosen aesthetic. The style of rocks you use will depend on what sort of a look you’re going for. Some rocks fit a particular aesthetic better than others, which may make them your chosen rock regardless of other factors.

Avoid Rocks with These Characteristics

Dirty rocks or rocks thick with pollutants should never enter your aquarium under any circumstances. If you’re finding rocks in nature, never take from a polluted waterfront, such as a public lake that has pollutants in the water. It is often not possible to thoroughly sanitize these rocks.

Rocks that are too heavy can pose a risk. Even though granite is a safe addition to your aquarium, you should be cautious about how you use it, as a simple fall can crack the glass.

If you decide to use these heavy stones, do not stack or balance them. Doing so increases the risk of them falling and breaking your aquarium.

Highly jagged rocks such as some slates also require caution if there will be fish in the aquarium. These can also be dangerous to clean, so make sure you watch where you’re putting your hands!

The final characteristic to avoid is rocks that heavily change the pH balance. Again, ensuring that your water doesn’t grow too alkaline or acidic is essential to protecting the life inside. Disrupting the pH balance can kill plant and animal life inside of the aquascape, making it arguably the most important thing to focus on.

Can You Buy Aquarium Safe Rocks at Home Depot?

Yes, Home Depot sells rocks that are safe to put in your aquarium. However, it’s still best to clean or rinse these rocks when you take them home. Manufacturing, shipping, and storage can cause pollutants to get on these otherwise safe decorative rocks, making them unfit for use until prepared.

Home Depot’s gardening section will generally carry many rocks that are safe for storage. These rocks are often sold in bulk, making it easy to get enough for a fantastic aquascape without breaking your bank. The selection in Home Depot will range and can usually change from store to store, so be sure to check several outlets if you don’t find what you’d like.

Before you go check out more fish tank decoration ideas here.


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