Choosing Aquarium Safe Rocks

My dragonet Daiyu, standing on live rock.

Rocks may not seem to do much, but in the aquarium they contribute to the ecosystem a great deal. Calcareous rocks in your aquarium raise pH and make your water "harder"; replicate marine habitat parameters. Rocks provide hiding places and breeding grounds for your fish, making them at home. Copepods, amphipods, and other micro-organism foods will cling to your rocks, which allows your fish to hunt and eat them. Algae will grow on your rocks so that if you have snails, crabs, shrimps, and other intertebrates, they will have a constant food source to fulfull their herbivore needs. Rocks can be structured into an aquascape, making plateaus, mountains, and decorations to transform your aquarium beautifully. Rocks near the top of your fish tank, closer to the aquarium lighting, will grow vibrant, astounding healthy algae of colors including light green, pink, red, and purple. As your tank ages, the colors will change, providing "seasons" in your fish tank. This makes your aquarium world really come to life! In marine tanks, rocks are essential to the saltwater habitat and ecosystem. In freshwater tanks, the pH and alkalinity buffering is not needed, but rocks will add fun and visual appeal to your fish tank. Read below to find out which rocks are the best for freshwater and marine aquariums.

Best Safe Freshwater Aquarium Rocks

Freshwater aquarium rocks should be inert, meaning they should have no affect on the pH or hardness of your fish tank water. Freshwater habitats are considered soft water, and adding the wrong rocks to your tank would sway your water to be hard; uncomfortable for your fish. An exception to where you can use calcareous rocks that do not contain salt is with African Cichlids and other hard water originating freshwater fish. The rocks type to stay away from is calcereous rocks; these rocks contain calcium and cause pH and hardness boosting in your water. If softer freshwater is desired, it is best to add clean wood which softens water. Inert rocks that look great in your freshwater tank are:

Aquarium rocks can cause harm to your fish and aquarium ecosystem if they are not cleaned before use. This is because dust, toxins, and harmful outside bacteria may reside on the rocks. If using pre-sterilized rocks from a pet store it is still recommended to brush them and soak them for at least one day to be sure they are completely dust and debris free. They may have gotten dirty by waiting on shelves or during shipping. If gathering rocks from nature, beware that there is always a risk. There is never a way to be one hundred percent sure that your rock will be completely clean, and it is unknown what kind of bacteria lives on the rocks. However, if taking rocks from nature, follow these steps to have the maximum fish tank safety possible:

Cleaning Rocks From Nature

Lava Rocks

Lava rocks are formed when volcanic lava cools. Over seven hundred types of lava rock exists, so lava rocks in stores may vary slightly in color shades. Lava rocks may be black or gray, but the most commonly sold lava rock is a cross between red and orange. These rocks are durable, as volcanic lava cools into a hard substance. Lava rocks are very porous, so they are good for breeding healthy bacteria in your tank. Usually, lava rocks come with a hole or two that fish enjoy swimming through. Overall, lava rocks are appealing visually, tank healthy, and entertaining while you watch your fish swim through the rock's holes. A great lava rock is as follows:

Lava Rock
Lava Rock
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Shale and Slate

Shale is a sedimentary rock composed mostly of clay, quartz, and calcite. This rock is usually long and thin, making it perfect for aquarium plateaus. This rock is hundreds of years old, and is very durable. Shale is perfect for aquascaping, and comes in a range of colors including black, gray, and purple.

Slate is a fine-grained metamorphic rock that is derived from shale. It is composed of mostly volcanic ash, quartz, and clay. Slate can be found colored in many shades of gray, green, purple, and cyan blue. Slate is very durable and like its counterpart shale, great for aquascaping as plateaus.
Both shale and slate can be found in many local fish stores, pre-sterilized. These rocks will be a great addition to any freshwater or marine tank.

Green Shale

Photo credit given to Flickr user James St. John.


Basalt rocks are igneous, volcanic rocks formed from cooled lava. Basalt rocks are very dark, usually gray scale rocks. These rocks are very heavy and dense. Basalt rocks come in various shapes; squares, rectangles, circular stones. They come in all sizes, big and small. Basalt rocks do not cause pH buffering, so they are suitable for both freshwater and marine aquariums. Basalt rocks may be found in nature or at a local fish store near you.

Basalt rocks

Quartz is a beautiful, transparent crystal gem that resembles the appearance of diamonds. Quartz is inert; it will not alter your pH or water hardness. Quartz comes in a variety of colors; amethyst is purple, citrine is yellow, rose is pink, smoky is black, and milky is white. Quartz is aquarium safe and is a great addition for any tank that wants some bling and uniqueness.

Basalt rocks
Plastic Aquarium Rocks

Plastic aquarium rocks are decorative rocks created to give aquariums a scenic look without the worry of rock finding and cleaning. These decorations come in many different forms; almost any rock you could think of. A positive aspect is that you can have any rock look you want; no need to worry if the rock type is suitable for your aquarium environment. The negative side is that you do not get the benefits of real rock look, texture, and bacteria growth. Decorative rocks may be found in your local fish store or on the internet easily.

Decorative Shale RockDecorative Texas Holey Rock
Decorative Shale RockDecorative Texas Holey Rock
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View on Amazon

Best Safe Saltwater Aquarium Rocks

Saltwater aquarium rocks imitate oceans by being calcareous: they raise the pH and hardness of your water. In marine tanks this is great, because the fish species have originated from bodies of saltwater and prefer hard water. Calcareous rocks can be huge, and used to create reefscapes in your tank. Marine fish enjoy love reefscapes, and will hop about them excitedly. They will hide behind, eat micro-organisms off of, and play on these rocks. In a marine tank, the rule to abide by for optimum fish happiness is 1.5 pounds of rock per gallon of tank water. These precious beings came from the reef, and to appreciate them we can give them a reef of their own to make them at home. Great reef rocks include:

Live Rocks

Live rocks are aragonite skeletons of dead corals that are harvested from wild reefs originated in the Caribbean or Indo-Pacific locations. Live rock can be told apart from base coral rock because it is covered with coralline algae colored mostly pink, purple, green, and red. Live rock is "live" with millions of healthy bacterias for your aquarium. Live rock in your aquarium should follow the guidelines of 1 to 1.5 pounds of live rock per gallons of aquarium water for maximum healthy water parameter impact. This number can be slightly more or less depending on personal taste and style. Benefits of live rock in your aquarium are:

Mature Live Rock

Photo credit given to Flickr user Moto "Club4AG" Mlwa.

Selecting live rock

Choosing live rock for your aquarium is based on appearances as well as best value and cleanliness. When purchasing live rocks at your local fish stores follow the below steps in order to choose the healthiest, most thriving rocks for your fish tank:

If there are no local fish stores near you selling live rock, or if you would prefer the ease of buying pre-picked live rock, Blue Life Aquatics offers a good deal of four dollars per pound of live rock rather than the usual five or six dollars:

Blue Life Aquatics Live Rock
Blue Life Aquatics Live Rock
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Curing Live Rock Before Use

This guide is for curing aquarium rocks in an established tank; a tank that already contains livestock and corals:

This guide is for curing aquarium rocks in a new tank; a tank that is not yet established and does not contain livestock or corals yet:

Dried Reef Rock and Petrified Coral
Beginner Live Rock

Dried reef rocks are essentially live rocks that are dead of bacteria and organisms. Dried reef rocks are composed of dead coral from reefs. These rocks are usually white to tan in color; no colorful coralline algae like on live rocks. These rocks are great for making aquascape structues for your fish to live in, hide in, and enjoy.

Petrified coral is coral that is dried and no longer houses living organisms or bacteria. Usually this type is coral is seen as white to tan branches. Petrified coral is great for adding unique features to your aquarium aquascape.

Both dried reef rock and petrified coral can be made "live" with bacterias and organisms with time and a healthy, thriving aquarium. A newly established tank may take years to gain large quantities of coralline algae and bacteria blooms because the tank ecosystem is new and must mature and gain stability to maintain small, delicate organisms such as copepods and various bacteria. The process of turning dried rock and coral "live" can be sped up by adding rocks, sand, and other objects to a newly established aquarium from an established, older aquarium. This way, the massive coralline algae and bacteria will spread onto your new rock and coral and house themselves there. Before adding dried rock and coral to your tank it is advised to cure them incase they have harmful dust or toxins residing on them from store handling. Proper curing method can be found above; "Curing Live Rock Before Use", but for a shorter duration of time. Dried rock and coral can be obtained at local fish stores or online for decent pricing. Great dried reef rock is sold by trustworthy Carib Sea. These rocks are white and shaped gorgeously, as well as having a cheap price of less than two dollars per pound:

Carib Sea Dried Reef Rock
Carib Sea Dried Reef Rock
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