The 4 Types of Substrate for Aquariums

The type of substrate for aquariums determines, to a large extent, the physicochemical qualities of the ecosystem. The right substrate depends on the species that inhabit the tank.
The 4 Types of Substrate for Aquariums
Ana Díaz Maqueda

Written and verified by the biologist Ana Díaz Maqueda.

Last update: 27 December, 2022

When building and designing a fish tank, many people have many questions about the right substrate for aquariums. What’s the best substrate for the tank? Will it clog the filter system? Are plants able to live in it? Will this type of pebble be harmful to the fish? Is substrate really necessary?

These and a myriad of other questions may arise when selecting the best type of substrate for aquariums. Below, we’ll tell you about the most common types of substrates. We’ll also explain their uses and the problems that could arise with each of them.

1. Sand aquarium substrate

Sand substrate for aquariums is one of the most common substrates, especially in combination with gravel, pebbles or large rocks. You can purchase sand substrate commercially in different sizes. Unfortunately, variants that are very fine can have several drawbacks:

  • They compact easily, which could create small, oxygen-deprived pockets where anaerobic bacteria that are harmful to fish grow.
  • High compaction prevents the root development of living plants. In addition, all types of sand are poor in nutrients, so no sandy substrate is good for plants.
  • If a fish stirs up very fine sand, it will remain in the water column for a long time, due to its low weight.
  • If you don’t have animals to move the sand, this should be done manually to prevent the formation of pockets without oxygen.

One of the greatest advantages of sand is that, when compacted, it prevents waste or uneaten food from being lost through the substrate and everything remains on the surface.

At the same time, there are fish that need a sandy substrate. Cory catfish, for example, have very delicate skin and love to forage on the aquarium floor. For this reason, it’s essential for a tank with cory fish to have a sandy or gravel substrate without sharp edges.

A rainbow crab on the sandy floor of an aquarium.
A rainbow crab on a sand-type substrate.

2. Gravel or pebbles

Gravel may be the most commonly used type of substrate in the aquarium world. It comes in a multitude of sizes and colors, from phosphorescent to more natural-looking shades.

The color chosen isn’t a disadvantage, as long as the water maintains all its parameters within the optimum range and the fish are well fed.

As with sand, the size of the pebble or gravel can also vary. The choice between one or the other will depend solely on the types of fish living in the aquarium.

For example, goldfish tend to nibble at the substrate and, if the pieces of gravel are as large as their mouths, they may swallow them by mistake and choke. The fish would die as a result of this.

On the other hand, many fish that spend the day foraging for food and debris on the bottom could have parts of their bodies damaged by sharp gravels. The injuries could become infected and threaten the animal’s life.

This isn’t to say that the gravel is bad for the tank, quite the contrary. It should simply be chosen correctly based on the aquarium’s inhabitants. To do this, you need to be very well-informed about the type of life of the species of animals that you want to introduce in the tank.

Gravel, unlike sand, is a good substrate for certain types of plants, which can easily cling to the pebbles. Also, although the gaps between stones are a source of debris accumulation, gravel is easy to clean.

The best thing to do is to have a gravel vacuum cleaner and every so often give it a good vacuuming to avoid the proliferation of potentially harmful bacteria.

A woman arranging pebbles in a shallow aquarium.

3. Specialized substrate for aquariums

The substrates seen so far–sand and gravel–are inert. This means that they don’t modify the physicochemical characteristics of the aquarium water at all. Specialized substrates, on the other hand, are those that provide certain characteristics or modify them. Among them, we find the following:

  • Aragonite: This type of substrate has the ability to prevent or regulate changes in the pH of the water. It also hardens the water, so it’s only recommended for aquariums with brackish water or one for African cichlids.
  • Vermiculite: This substrate is good when you want to have an aquarium with many live plants, as it’s rich in potassium and magnesium.
  • Peat: This substrate greatly lowers the pH of the aquarium, so the fish that live in it should live well in acidic water. It’s a very good substrate for plants, but it releases a lot of nitrogen -toxic to fish- and makes the water very dirty.

Specialty substrates are best for those experienced aquarists who are looking for some kind of specific result within the aquarium. It’s best to start with inert substrates or no substrate at all.

A hand holding specialized substrate for aquariums.

4. Bare bottom aquarium

That’s right, you can set up an aquarium without any substrate at all! Like all substrates, a tank without substrate also has its advantages and disadvantages. For example, the main disadvantage is that you can’t introduce any fish or animals that like to live attached to the bottom of the tank.

Having no substrate makes it much easier to manually clean the bottom. However, there’ll be no proliferation of beneficial bacteria in the aquarium and all parameters will have to be adjusted manually.

It’s true that most of the beneficial bacteria grow in the filter, but a good part of it also grows on the aquarium bottom. Without substrate, this isn’t possible.

At the same time, aquariums with bare bottoms are usually less attractive and, in addition, many fish can become stressed by seeing the reflection on the bottom. In general, this type of tank is reserved for breeding facilities or hospitalization areas, when a fish has a problem and must take medication.

An empty glass aquarium.

All substrates – and non-substrates – can be both good and bad. The best way to choose a substrate is to research and do some research about the animals you want to have in the tank. If you do this, it’s very difficult to make a mistake.It might interest you...
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