Can I Use Outdoor Gravel In An Aquarium?

Yes, you can, but you have to understand that outdoor gravel comes with risks. So before actually using your hand-picked stones, make sure that you clean and test the stones. The rock composition tends to change your aquarium water’s water hardness and pH level, which can be harmful to your fish. Stones collected outdoors are also usually covered with bacteria and contaminants.

But in general, as long as you scrub the stones clean from any biological material and get it tested, these rocks should be safe for your aquarium. All water-worn rocks that you get from the ocean are also safe for your tank.

How do I test the outdoor rocks and gravel?

The main threat of using outdoor gravel and rocks in your aquarium is the possibility of these rocks having calcium, which can modify your aquarium water’s pH. SO it is important to test these outdoor stones first before putting them in.

The first step is to thoroughly wash the gravel and stones to remove the grit, dirt, and contaminants. Testing for calcium can be done in a variety of ways.

The first method is by using vinegar. Using a few drops of vinegar, drop it on the rock or gravel, and if the vinegar is an acidic substance, foams, or fizzes, then you can’t use the rock. The foaming or fizzling is an indication that the rock has calcium on it. A second way to test it is to submerge the rocks and gravel you are testing with your current aquarium water.

Before doing this, get the initial hardness and pH of your aquarium water. Leave the gravel submerged for a week and after that, re-test the water. If the pH and hardness significantly increased, then don’t use the gravel to give you problems in the future.


What are the different kinds of aquarium gravel?

Aquarium gravel falls under the gravel size of about 2mm to ¼ inch in diameter, roughly similar in size to a dried pea. There are several kinds of gravel that you can choose from to use in your aquarium. You can also use a combination of this gravel because it is generally safe for all fishes.

The first type of aquarium gravel is the live gravel that comes from freshwater. With it comes microorganisms and bacteria.

The second type is the natural or river gravel, and as the name suggests, these are collected from the riversides and riverbanks and sometimes out of gravel pits.

Natural gravel usually goes through a cleaning and processing method so it can be ready for commercial use. It has an almost uniform shape and size. The edges are also smooth but are not coated with any sealant. Another option would be clay gravel, perfect for planted freshwater aquariums. This type is mineral and iron-rich, which is beneficial to plants.

Lastly, you can use artificial gravel. These are made from industrial resin or sometimes also from silica. Some artificial gravel is also natural gravel but is sealed with acrylic coating.

What are gravel and rocks that I should avoid?

For starters, rocks and gravel that are highly calcareous or stones with high calcium content should be avoided. You should also not use sharp-edged rocks as these can harm your pet fishes. Water washed gravel that has smooth sides are best. Here are the rocks that should not be used: Crushed corals or shells, geodes, limestone, dolomite, and marble.

What is considered safe gravel and rocks?

Putting in safer rocks in your aquarium like slate, granite, quartz, onyx, and ground glass shouldn’t give you and your fish problems in the future. You can also use some lava rocks so long as you make sure that you sand or remove the sharp edges because there are particular fishes like the Corey species that have extremely sensitive barbels.

Sandstone is also considered safe, but it is highly recommended to test this first to ensure zero traces of limestone. Most of the rocks and gravel contain not just a couple but a mixture of minerals. A single stone can have tens of minerals on it, so even if you identify it as one of the safe stones, test to make sure.

Where do I find outdoor gravel and rocks?

Just like the name suggests, Outdoor rocks and stones can be collected and found in the great outdoors. Since it is from Mother Nature, it is ideal for free. The best places to get outdoor gravel intended for your aquarium would be in lakefronts, oceans, and beaches. You can also search in dry wash beds and along the river banks. A word of advice, do not collect gravel and rocks from underwater locations, specifically protective environments. Removing these can disrupt the native homes and habitats of the plant life and wild fishes there.

Can I buy it instead?

You sure can! It is easier and sometimes more convenient too. You can get outdoor stones from different garden centers and plant nurseries in your area. There are also landscape companies that offer river rocks and other aggregates that you can also use in your aquarium. Alternatively, you can also check your local home improvement centers, especially those that sell gardening supplies.

Gravel and rocks bought commercially usually come in cheap and with more attractive options to choose from. Just make sure that after selecting your choice of gravel and stones that you still test them before you put them in your home-based fish tank.

Why Do I Need Gravel In My Aquarium Anyway?

A new hobbyist might reason out that it is purely for aesthetics purposes only. While this is true, there are other factors why you need to put some gravel in your aquarium. Gravel becomes the anchors for the roots of the water plants that you put in the aquarium.

Plants are a great addition to the small ecosystem you are building because it helps balance the water chemistry and serves as an additional source of oxygen to the water.

Aside from this, graven also serves as a home for good bacteria. These bacteria help break down the ammonia from your fishes’ urine and the nitrates from their wastes. They then convert these into 100% nitrates that are considered less toxic for your fish friends.

aquarium sand

What are the drawbacks of using gravel?

Gravel doesn’t have too many drawbacks when you use it in your aquarium. It is a practical choice for anybody who has a small ecosystem at home. The only main challenge – but a workable one – in using gravel is it harder to remove toxic blue-green algae should you encounter any outbreak. Sandy substrates would usually limit these outbreaks, but gravel allows the algae to thrive and grow and, if left untreated, can be hard to treat. This would be more challenging if you are using the porous kind of gravel.  

Is colored gravel safe?

A pop of colorful gravel can make your aquarium pretty and more attractive. If you want some colored gravel inside your aquarium, make sure that you select colored gravel that has been crafted with a polymer seal. The dyes used for the stones can be harmful to the fishes, especially if they bleed the color. So dipping the stones or brushing them with a polymer seal will help prevent the dye from bleeding and staining the water. It seals the color and protects your small underworld life.

After adding colored gravel, my aquarium water’s pH level increased. Why?

Most of the colored gravel, specifically the angular and rough-textured ones whose coating is powdery, are finished from white dolomite. This is a mineral healthy in calcium, increasing your water’s hardness level, alkalinity, and pH levels.

How much gravel do I put in my aquarium?

This is a much ongoing debate because this is a little tricky. Gravel is typically sold in weight, but when putting it in an aquarium, weight becomes void, and it is the depth that you focus on. An expert hobbyist would recommend that for sand, a depth of one inch is adequate, but it needs to be 2-inches to 3-inches in depth for gravel. If you want an equation for it, you find out the total volume you need and multiply that with a liter’s weight.

Can I use gravel of varying sizes?

Yes, you can, and the results are aesthetically pleasing. Just expect that sooner or larger, the larger grains will rise on top of the finer ones.

How can I keep my gravel clean?

The most convenient way of keeping your gravel and overall your tank “ocean bed” is by regularly using gravel cleaner. You can also use the old school syphon cleaner so long as you can manage not to drink your tank water by mistake.

How do I use a gravel cleaner?

Most syphon-powered gavel cleaners are intended to get rid of dirt-laden water from within your gravel when performing a fractional water change. Usually, this is done every week. You can vacuum 90% of your tank base without the need to remove all the water. Getting rid of a quarter of water should be enough for you to use the gravel cleaner.




Rita Wagener
Rita is a resident paw expert at Pet Keepers. A registered & licensed dog trainer, she also has a degree in animal nutrition, and runs her own dog training course.

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