There’s plenty of fish in the sea. What’s in your aquarium though?

Besides the fish and other sea creatures that you put in your home’s aquarium, you’ll also need aquarium gravel & substrates. Knowing the difference between the two is essential to your home aquarium functioning well. For a beginner’s guide to aquarium gravel & substrates, read on.

What Are Aquarium Gravel & Substrates?

So, your brand-spanking new home aquarium just arrived and you can’t wait to find your very own Nemo, Dory, and Marlin to drop into your mini-ocean. Whether you knew it or not, before you even fill your aquarium with water for your fish, you need substrate.

The substrate is any of the loose material that’s on the floor of your aquarium tank. It can be the pebbles or any other loose object covering the bottom.

Gravel is a kind of substrate consisting of pea-sized pebbles between 2mm and 5mm. With gravel, the gaps around the pebbles are smaller so that feces and food can’t fall as far. You can easily remove food with a gravel vacuum.


  • is far and away the most common substrate;
  • looks natural; and
  • is multi-colored and variously sized.

Don’t get sharp-edged gravel, especially if your fish sift or dig through the substrate. Also, don’t get it if you have catfish since its roughness can damage the skin of scaleless catfish. 

What Are the Differences Between Aquarium Gravel & Substrates?

While gravel is, in fact, a kind of substrate, there are some differences between the two.

Consider the other kinds of aquarium substrates, besides gravel, like large river rock. This kind of rock can be used on top of gravel or without it. It looks good and natural.

If your tank has live plants, then use vermiculite or laterite as substrate. These substances will hold and release nutrients for your plants. Simply cover them with a layer of gravel.

Sand is another kind of substrate. From fine to coarse sand of all kinds of colors, sand is a common substrate. It’s also the most natural substrate because it replicates the muddy, silty, or sandy environment from which most of your fish came.

There’s also soil; substrate soil, to be exact. Substrate soil is designed to not mix with water and thus make muddy water. Only use substrate soil in tanks with live plants growing.

Last but not least, some substrates can change your tank’s water, just like the vermiculite and laterite mentioned above. When you deliberately add them to your aquarium, you’ll see benefits. These water-changing substrates include:

  • Peat, a water-softener; and
  • Aragonite, which buffers the water to stop changes in the pH level.

The previously-mentioned nutrients that vermiculite releases are magnesium and potassium.

If you want to get even more scientific, biochemistry has what’s called an enzyme substrate.  

Substrates: The Foundation of Your Aquarium

As you now know, the foundation of your aquarium isn’t the water or even your lovely fishes: it’s the gravel and substrates. These elements come before anything else you put into your aquarium tank. Keep in mind that there are some key differences between aquarium gravel & substrates.

For more advice on how to make your home as comfortable as possible for your fishes or other pets, explore the rest of the Pets & Animals section of our site.