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How to find and put rocks in your fish tank

One of the more popular decorative items you can use when it comes to stylizing your fish tank are rocks.

This guide at Aquarium Blueprints will lists out the benefits of using aquarium rocks as well as rather or not you can use the ones you find outdoors.

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Benefits of Aquarium Rocks

Provide surface area for beneficial bacteria to grow

Having rocks in your aquarium will provide plenty of surface area for beneficial bacteria to grow on. You need these colonies to oxidizes the otherwise harmful ammonia and nitrite compounds that come from organic wastes such as fish excrement and decomposing fish food.

If you want as much surface area as possible, you should look into getting rocks that are porous. This is because the small holes add a lot of surfaces for the bacteria to settle on.

Make natural looking caves

Depending on the rocks you pick out, you can create a lot of natural looking caves by stacking them together in your fish tank. Caves are great as they provide shade and hiding spots for your fish, especially if one is getting harassed.

Furthermore, smaller caves are essential for fry and/or shrimp. If you are planning to breed fish and shrimp in a community tank, then we highly recommend creating multiple caves by stacking rocks so that they won’t get eaten and/or harassed to death.

Can be attached to live plants

You can also attach live plants to the rocks, which will obviously keep them in place. Certain plants (such as Anubias, Hornwort, Java Fern and Java Moss) don’t need a planted substrate as their roots will consume nutrients straight from the water column. You can attach these to rocks to hold them in place.

To attach the live plants to rocks, we recommend the Seachem Flourish Glue, which you can find on Amazon with this link. The product uses cyanoacrylate gel, which is safe for underwater use. It will also bond within seconds, which means that you don’t have to wait long before being able to put the rock, with the live plant attached, into your tank.

Enhance the look of your tank

By making caves and being able to attach them to live plants, you will be able to create a lot of nice looking rock-based decor in your tank. If you want your aquarium to look like it is part of nature, then we recommend decorating it using rocks.

Do rocks affect water parameters?

Certain types of rocks will affect your water parameters if your tank water is acidic. These include Black Pagoda, Frodo Stone, Grey Rocks Elephant Skin, Limestone and Seiryu Stone. These rocks will leech elements into your water column, which will result more hardened water in addition to an increase of pH.

This process generally happens slowly enough that your fish will be able to adopt to the changing water parameters over time. With that said, if your water was very acidic and you want to add a huge amounts of rocks, then a dramatic change in pH could cause your aquatic pets to go into shock, which may result in illness or even death.

Therefore, we recommend playing it safe as you should look for stones that won’t leech anything into your tank water. Before buying rocks, you should definitely do some research in this area.

The best places to buy aquarium rocks

When buying rocks for your fish tank, we highly recommend checking out your local fish store. That way, you will be able to personally select the shapes and sizes you want. Some stores, such as the Aqua Forest Aquarium in San Francisco, even set up a small station where you can stack the rocks to give you an idea of what they will look like in your tank.

If you can’t find the rock type and/or size you want locally, you may want to try ordering online. Buying over the internet does come with some risks as the stones could break during shipping. Not to mention that the rocks may not look like the ones that are shown in the picture. So make sure you carefully look at the reviews of whoever you decide to buy from so that you will know you are getting the products from a reputable source.

Can you use rocks found outdoors for your fish tank?

Buying rocks can be expensive, especially if you have a big aquarium. As an alternative, you can try collecting rocks outdoors.

Before, running out and collecting every stone you can find, you first have to make sure that it is legal to take them in public spaces. Otherwise, you could get in some troubles with the authority if you get caught red handed.

If you are in the clear, we recommend collection rocks near bodies of water. For freshwater, try to collect near freshwater lakes, ponds or rivers. For saltwater, try going to the beach.

To make sure that the stones you are collection won’t leech into the your water column, we recommend doing a little experiment. Pour some muriatic acid (if you don’t have the solution, you can purchase it on Amazon) onto the surface of the rock. If you see some fizzles, then it means that the rock will most likely leech its contents into the water in your tank. As a result, we advise looking somewhere else. If there is no reaction, then the rock is most likely safe for aquarium use. You can watch a video of The King of DIY on how to determine which rock is suitable for aquarium use below:

Before putting the rocks you found into your tank, you first have to thoroughly clean them. To do so, we recommend using a high pressure hose to clean off as many loose particles as possible. Afterwards, you should dip your stones into hydrogen peroxide (which is available on Amazon with this link if you don’t have one on hand) for around an hour to kill off the bacteria.

To kill off even more bacteria, you might want to consider putting your rocks through intense heat. You can do so by either boiling them with hot water or heating them up via an oven. A temperature of around 200 degrees for approximately 30 minutes should be enough to disinfect a majority of bacteria.

Keep in mind that heating your rocks intensely could result in them exploding. This is especially true for porous rocks that have a lot of holes. For that reason, we recommend avoid using an oven altogether.

Instead, you should use a steel pot, put your rocks in and then pour the boil water. Quickly put the top of the pot on and then something to weigh it down so that it won’t easily fly off if something does explode from within. As a precaution, you may want to boil your stones away in a big open area just to make sure no one gets hurt as well as no property gets damaged.

As you can see above, collecting your own rocks for aquarium use is a lot of work. So, if you have a choice, we definitely recommend you just buy the ready-made fish tank ones.


Aquarium rocks are great as they provide a lot of surface area for your beneficial bacteria to grow. They can also be use to create natural decors for your fish tanks.

We recommend buying the stones from your local fish store if possible as the rocks can break during shipping if you opt to purchase online. Not to mention that you will be able to handpick what you want at the shop.

While you can try collecting the rocks for aquarium use, it takes a lot of work. Thus, we only suggest you do so if you have no other option.