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Types of Aquarium Substrate and Their Purpose

More than just pebbles at the bottom of the aquarium, choosing the right substrate for your aquarium can be like choosing the right paint color for your walls. But substrate goes well beyond just being appealing to the visual aspect of your aquarium.

Yes, in most circumstances substrates provide a complete, more natural appearance to the aquarium, but it has a more important role than just looking pretty. The substrate provides a large surface area for beneficial bacterial to colonize and grow. These bacteria aid with the breakdown of detritus and fish waste, keeping the aquatic environment safe for all your finny friends.

Not just a great place for bacteria to grow, substrates may also help reduce stress. Substrate provides aquatic life a sense of orientation. It prevents the bottom from creating a mirror-like base in which the fish sees a reflection of itself and others. Additionally, there are also species of fish and invertebrates that enjoy foraging and borrowing into the substrate, some even make a cozy bed under it at night.

Live plants benefit from a layer of substrate which creates an area for nutrients to accumulate and their root systems to take hold.

Substrate can also be utilized for breeding as there are species of fish, like cichlids, that will make a nest in the substrate to lay their eggs and rear their young. 

Freshwater Aquarium Substrates

So what freshwater substrate is the right one with all the choices out there?

One of the most common types of substrates is gravel. Gravel comes in an array of colors and sizes to meet the needs of most freshwater aquarists and does not alter water parameters. Some are epoxy coated to prevent the color from fading over time while others are natural rock. Larger natural stones, like river rock, are sometimes utilized and make a good substrate for larger fish that like to rearrange the décor.

Another substrate growing in popularity is sand- although not play sand from the hardware store. Play sand is silicate based and will contribute to brown algae blooms. Sand sold for freshwater aquarium use is usually coated to prevent silicates from being released. Sands are a great option for fish that like to borrow and scavenge for foods. Some cichlid pet parents utilize sand substrates as it mimics their natural environment. Some will also ingest some sand during feeding which aids with their digestion. One concern with sand to be aware of though is that the development of hydrogen sulfide can occur if the grain is too small.

Many plants, which obtain their nutrients from the water, can grow in gravel and sand substrates, but the use of specific plant substrates will help plants flourish that obtain nutrients through their roots. These substrates consist of compounds like soils, volcanic rock, and baked clays which help plants thrive. 

Saltwater Aquarium Substrates

Marine substrates differ a little from just gravel. While you could utilize gravel in a marine aquarium, over time you may have an issue of keeping the pH stable. Marine substrates usually consist of materials high in calcium, like crushed coral, aragonite and oolitic sand. This calcium carbonate is what helps to buffer the water, maintaining a higher pH.

When choosing the right marine substrate, whether you have a reef system or fish only system will help determine the grain size of your substrate. Since fish only systems do not have as much flow as a reef tank, you can utilize a smaller grain size, since it will not be pushed around. In a reef aquarium with a lot of strong water current, you will want to choose something a little larger and heavier. The species of aquatic life you want inhabiting your aquarium may also alter your choice of substrate. Many wrasse species burrow for protection and to sleep; a coarse sand will not allow them to do this freely, so choose a fine sand substrate. Additionally, there are species of snails, like nassarius, that burrow into the sand to scavenge for food, so be sure to do your research when selecting a substrate.

How Much Substrate Do You Need?

This is determined by the size and shape of your aquarium, as well as how deep you want your substrate. As a general rule, 1 pound of substrate per every gallon of water should provide approximately a 1” deep substrate layer.

If including plastic plants in your setup, you may want to make the substrate a little deeper as this will allow for the base to be secure. Live plants will require a 2- to 3- inch substrate depth. There are species of plants, like Anubias, that will do fine without any substrate, but larger plants will need the deeper layer to ensure there is sufficient room for their larger roots to branch out.

Be cautious to not have your substrate too deep as it can create pockets of organic waste that produce toxic gases due to the inability of oxygen to reach it.

Reviewed by Don Spaeth, Petco’s National Aquatic Care, Education and Programs Manager

Don is Petco’s National Aquatic Care, Education and Programs Manager. He is an avid aquarist who has worked with and cared for freshwater and marine aquatic life for over 40 years. Throughout his 27+ years with Petco, Don has actively been involved with our aquatic vendor partners and worked to promote aquatic education both in store and company-wide.