How To Choose the Right Aquarium Substrate

Everyone knows that setting up a “good” aquarium requires certain essential elements. You’ve got to choose the right combination of fish, establish the correct water parameters, and select appropriate decorations to keep things interesting, both for you and your finned friends. 

Something that many novice aquarists fail to include in this list of essentials is “appropriate substrate.” And we can’t blame them, either. Choosing what to cover the bottom of your tank with is up there with choosing a filtration system for the prize of Most Boring Part of Designing an Aquarium. 

And yet, it is a critically important decision.

Why Does Substrate Matter?

Much like the flooring in your home, substrate–the material that lines the bottom of a tank–is a constant part of your fishes’ lives.

As you might have noticed, not all tanks have something lining the bottom. Technically, you don’t have to use a substrate in an aquarium. People commonly choose to display a particularly rare or prized aquatic specimen in a bare tank so that nothing detracts from its splendor. 

Most long-time aquarium hobbyists, though, consider it best to include at least a little something for the fish to look at and play with. 

If you decide to use it, the substrate you choose can directly impact your fishes’ health and happiness.

The Benefits of Using Substrates

The first and arguably most immediate benefit of using an aquarium substrate is that it provides orientation for your fish. Tanks that lack substrate can stress the fish inside them, particularly if the tank is lit from above. The light that reflects off the mirrored tank bottom can irritate and confuse them. 

The second benefit is that a substrate provides a surface for bacteria to grow on. While this might sound like a drawback, we are referring to the beneficial bacteria that help maintain the water chemistry and cleanliness of your tank. 

Such bacteria convert the ammonia and nitrite that fish expel in their waste into nitrates, a process you may have learned about in school, known as the Nitrogen Cycle. Both nitrite and ammonia are toxic to fish in large quantities, so these bacteria play a critically important role in keeping your tank water clean.

A third reason to use substrate is to create a more natural look for you and a more natural feel for your fish. Aquariums that lack substrate are rather striking in appearance. 

While that is usually the effect that people who set up their tanks in that way are going for, it’s not necessarily ideal for something you will probably spend many hours of your life looking at. Plus, your fish will appreciate a set-up that replicates their native habitat as closely as possible. 

Substrates also give your fish something to play with. While some species will find this more important than others, all fish can benefit from the presence of something to push around or dig into from time to time. 

Substrates also provide anchoring for live plants. Not everyone wants live plants in  their tank, and some people prefer their plants in pots. But if you are inclined to create such a natural environment for your aquatic friends, you’ll need a substrate. 

Additionally, certain substrates can produce more vivid coloration in some fish. This effect is purely aesthetic, and your aquarium will do fine without it. It’s nice to know that you have the choice to amp up the colors, though.

The Drawbacks of Using Substrates

There are few reasons to not use any substrate in a tank. Certain types do have particular drawbacks, though. 

The most important thing to be wary of is how the substrate you choose will affect your tank’s water chemistry. Certain types (discussed below) contain minerals that alter the hardness and pH of your water. 

Many fish have strict requirements for their water chemistry and don’t tolerate changes well. In extreme instances, water chemistry changes can kill your fish. 

Light-colored or reflective substrates can also potentially affect your tank denizens. At the very least, some fish will react to a light substrate by blanching. The theory behind this is that it’s dangerous for them to stand out too much against the background of their habitat. 

Most natural habitats tend to have a darker or subdued color tone, and this is what your fish will most likely feel most comfortable with. Blanching can also be a reaction to stress, which your fish may experience if their substrate is reflective. 

One last drawback to mention is that substrates are more difficult to clean than a bare tank. Cleaning difficulty varies widely, depending on which substrate you choose, but all require some sort of care to avoid problems. 

At the very least, using substrate means that you have more work to do. In some cases, certain types of substrate provide places for food and waste to accumulate. This accumulation will lead to the dreaded and deadly nitrate buildup if not fastidiously maintained.

What Types of Substrate are Available?

These days, you have quite a few options to choose from. 

Gravel is, by far, the most popular choice. It comes in many sizes and colors, thus giving you lots of options to create the perfect look for your tank. There are even glow-in-the-dark gravels for the really adventurous aquarium designer. 

Sand is another common and coveted substrate. Its beauty, fluid lines, and association with the beach make it a popular choice, although it requires significantly more maintenance than other materials. 

Crushed coral, limestone, marble, shell, and other organic materials are less popular than sand or gravel because they affect the pH of your water, which many fish can’t tolerate. Some, though, such as cichlids, actually prefer a higher pH. 

River rocks are a favorable choice for a more “natural” look and glass marbles give off a whimsical vibe. Neither is very practical for cleaning purposes, though. Glass marbles can also stress your fish if they reflect too much light. 

If you plan to have a planted tank, there are several specialized options to consider. One is fluval substrate, also known as fluval stratum. This is a type of volcanic soil collected from the foothills of Mount Aso in Japan. Laterite is another possibility. 

It is composed of weathered clay from tropical or subtropical areas. Instead of releasing minerals for the plants, as most planted substrates do, it holds them in storage until they need them. 

The third option for a planted aquarium substrate is vermiculite. This is a mixture of aluminum, iron, and magnesium, which slowly releases important nutrients for the plants. Aquasoil is another variety of planted substrate. It is composed of soil baked into small, hard granules and aids greatly in plant growth, although it does break down over time.

There are also many planted tank substrate mixes on the market, all of which claim to be “the best” combination of several organic materials.

How to Choose the Right Substrate

Choosing the right substrate depends on multiple factors. Which factors are relevant to you depend on what kind of tank you plan to have. 


You have a wide range of size options to choose from when designing your tank. You can opt for tiny sand particles, large river rocks, or anything in between. Most beginners tend to choose a medium-sized gravel substrate. This choice is visually pleasing without being too difficult to clean or providing too many places for food to accumulate. 


Aquarists commonly divide the many different types of aquarium substrates into inert and non-inert. Most material is inert, meaning that it does not alter the water chemistry in any way. Such materials remain largely unchanged over time; they either break down extremely slowly or not at all. 

Inert substrates are principally composed of natural materials such as gravel, baked clay, or sand. None of these types contain any significant amount of nutrients. This is important if you plan to include living plants in your aquarium environment. 

Non-inert substrates, on the other hand, affect water chemistry. This effect is not necessarily a bad thing. Some fish, particularly those from the Amazon River Basin area of South America, prefer a lower pH. 

Cichlids, on the other hand, thrive in a more alkaline environment than most species prefer. Driftwood, peat moss, and various planted substrates all lower pH levels. Crushed coral, limestone, and dolomite gravel, on the other hand, will raise pH levels. 

This decision largely depends on what type of aquarium you want to have. If you plan to have living plants in your aquarium, you will have to consider their requirements, as well. The best type of substrate for a planted tank will be different from the best type for a fish-only tank.

Ease of Cleaning

Some materials are much more high maintenance than others. All substrates need to be cleaned regularly, but each type has its quirks that you must attend to in order to prevent water chemistry problems. 

River rocks or other very large materials allow a lot of waste material and excess food to fall into the crevices between the individual pieces of substrate. This residue cannot be easily suctioned out with your average daily or weekly tank maintenance, which leads to buildup. 

Such buildup will eventually create a cloudy tank and lead to water chemistry imbalances, algae, growth, and other unwanted results that require a lot of time and money to fix. 

Sand, on the other hand, has individual particles that are so small that any unwanted material usually sits right on top of the substrate, just waiting to be cleaned off. While this might sound perfect, it’s not. 

The minuscule size of sand particles also means that they easily get sucked up into your tank vacuum when you do routine cleaning. Even if you simply disturb the sand without vacuuming it up, floating particles can easily get sucked into the main filtration system instead of settling back to the bottom.


How will your aquarium look with a particular substrate?

This is a big consideration that some people fail to give adequate thought to. 

Sure, you can choose that blandly colored gravel that’s on sale at the local fish store, but it won’t make anything pop. 

On the other hand, a neon orange gravel will certainly draw your attention when you walk into the room. But how will your fish look against it? And will that huge pirate ship decoration that you just invested a lot of money in go well with it?

The combined look of substrate + fish + decorations should be thoroughly considered before you invest your money in something you’re (hopefully) going to be looking at for a long time. 

Some people advise trying to replicate a natural environment as much as possible with sand or plant-friendly substrates, muted decorations, such as driftwood, and live plants. Others will tell you to choose a substrate that will make your fish “pop.” In other words, dark-colored fish should have a light-colored substrate and vice versa. 

At the end of the day, you have to decide what is most visually pleasing to you because there are as many opinions out there as there are people to give them.

Requirements of Your Fish

Let’s not forget what the guys and girls who will be living in this tank need, either. Just as different people have different requirements for happiness, so do different kinds of fish. 

We mentioned above that African Cichlids need a more alkaline water chemistry than most other freshwater fish. They aren’t the only ones with special needs. 

If you plan to have bottom-dwellers, particularly those without scales (such as catfish), you will want to avoid sharp substrates, such as certain gravels. All bottom-dwellers have at least one pair of delicate barbels around their mouth areas that they used to feel along the ground for food and to guide them. These can easily get cut or otherwise damaged by sharp substrates.

Similarly, many species of fish are diggers or nest-builders. They will also need a softer-edged substrate to do their business in. Some species require substrates that can fit inside their mouths. Such fish take individual pieces of aquarium gravel or small quantities of sand or other substrates in their mouths to move them around the tank.


If all of this information seems overwhelming, we understand. There is a lot more to think about regarding fish tank substrates than many people realize. 

The good thing is that there is so much more information freely available for the aquarium hobbyist today than there used to be. With a quick search of the internet, even the most novice fish owner can find just about any answer that  they might need. 

If you need more help than what the internet can provide, you can always consult the knowledgeable people who work at your aquarium supply store. First-hand knowledge is invaluable for some of the finer details of maintaining a complex aquatic environment for a variety of living creatures. 

While it is important to choose an appropriate substrate for your aquarium, remember that that is only half the battle. Consistent maintenance and monitoring are also necessary to keep everything and everyone happy and healthy. 

So, swim on, fish lovers, and make those tanks fabulous from the substrate to the stars!

Johanan Viljoen

Johanan Viljoen