How Much Gravel Does An Aquarium Need?

-- By Carol

If you are a fish owner, the question of how much gravel or substrate should be put in a fish tank must have come to your mind at least once.

Gravel or substrate is extremely important for your aquarium.

So, whether you’re a new aquarium owner or an experienced one – here’s a complete guide on how to calculate the amount of substrate for your aquarium and how often you should change the gravel.

For those who aren’t aware of what substrate is – it is a layer at the bottom of a tank. It can be sand, aquarium soil, and rocks, but it’s mostly gravel.

Putting together an aquarium is not a very difficult task, but you need to be aware of a few things.

Table of Contents

Why Is Substrate Used in a Fish Tank?

The most common substrate used in a fish tank is gravel.

But why is a substrate required at all? A substrate is not just used for aesthetic purposes; in fact, it sits at the bottom of the tank and plays a crucial role in maintaining a healthy aquarium.

Another reason a substrate is used is to establish the depth of the fish tank.

The type of gravel you choose is majorly determined by the type of fish you have in your aquarium.

While some fish prefer finer gravel, others may flourish with a more coarse type of gravel.

Many fish like to forage or dig into the bottom of the tank; to prevent this, you can use a heavier type of gravel.

Lastly, you need to consider what will be added to the aquarium.

This includes plants, rocks, decorations, etc. Certain plants require a specific type of substrate.

What is Gravel?

There are different kinds of substrate available that are used as a base in aquariums or fish tanks.

The most popular substrate used as a base layer is gravel.

Gravel is made up of rock fragments that range from granules to boulder-sized pieces.

Gravel has larger pieces as compared to other substrate materials, making it very porous.

Since it’s heavy, it remains intact for longer and is also very flexible.

Gravel is available in different grades, ranging from coarse to very fine, depending on the type that you want.

Especially aquarium gravel is safe to use as it doesn’t spread anything into the water – making it neutral.

However, gravel is a very porous material that makes it easier for fish food and excretion to sink to the bottom and rot easily.

So, it needs to be maintained and flushed out or vacuumed at the very least.

It doesn’t matter what type of base you use, the depth of the gravel is usually between 1 and 3 inches.

When trying to figure out the quantity of gravel required for fish tanks, try to take into account the needs of the fish, hygiene maintenance, and minimum depth.

We will discuss these factors in greater detail later on.

Using Gravel for a Fish-Only Aquarium

Gravel is used in a fish-only tank and its main purpose is to provide a beneficial bacteria bottom for the aquarium.

The fundamental purpose of a substrate or gravel was to allow bacteria to grow and build colonies within it.

Establishing and maintaining a balance of healthy bacteria in the aquarium will help your fish thrive in the water.

Another basic reason for using gravel is that it provides an orientation to the fish.

If there is no base layer— such as substrate— present at the bottom of the tank, the glass and reflections will disorientate the fish causing extreme amounts of stress and even death.

If you’re using gravel only for these basic purposes in a fish-only aquarium, then a depth of 1-2 inches of gravel will be adequate.

In case you have bottom feeders with the tank, you should add more depth to the gravel while making sure that the substrate is fine rather than coarse.

Even for basic use, the coarseness of the gravel is a huge factor.

What Factors to Consider When Using Gravel in Aquarium

When you’re deciding the type and the quantity of gravel that is required for an aquarium, there are certain factors you most definitely should consider.

Here are the factors you should consider:

Type of Fish in the Aquarium

The fish you intend to put in your aquarium will highly determine the type of gravel you’ll need and the quantity required.

While some fish prefer coarse gravel as they can mess around in it, others prefer finer gravel in which they can dig and forage.

In order to determine the quality and quantity of gravel, figure out the kind of fish you’ll be keeping in the aquarium and research to find out their preferences.

Plants in the Aquarium

Another major factor that will help determine the quality and quantity of gravel is the plants you’d prefer to have in your aquarium.

Plants without a root system are least bothered by the type of gravel in the aquarium as they draw their nutrients from the water.

However, rooted plants are most definitely affected by the kind of gravel being embedded at the base of the fish tank.

Big rooted plants require a very deep layer of finer gravel.

This is because large plants will be heavier on the top, and they require a significant amount of nutrients, which means they need a reasonably thick layer of gravel.

Small plants, however, tend to have smaller root systems and therefore, can easily survive with a shallow layer of coarse gravel.

Size and Decoration of the Aquarium

The size of the aquarium, its dimensions and the total number of gallons it can accommodate will determine the requirement of gravel at the bottom of the tank.

The bigger the aquarium, the more gravel will be necessary.

Many people choose to decorate their aquariums to beautify them.

They add plants, colorful rocks, sand, and seashells.

They usually opt for natural-looking gravel. From an aesthetic point of view, the more decorated the fish tank, the better the gravel will look.

Additionally, for heavy decorations that need to be anchored down, you will require a significant quantity of gravel.

How Much Gravel Do You Need For Your Aquarium?

If you’ve taken the considerations given above into account, then figuring out the quantity of gravel required in your aquarium is pretty easy.

For starters, 2 inches of gravel is great as a base for a freshwater aquarium. 2 inches is the minimum amount of gravel required as a substrate.

As we mentioned, another important factor to consider is the dimension and size of the fish tank.

The size of the aquarium must be exact. It is a no-brainer that the bigger the size of the tank, the more gravel will be required to form the base.

To calculate the exact amount of gravel required, you will multiply the depth of the aquarium by inches by the amount of gravel you have calculated per inch.

You can also use an Aquarium Gravel Calculator to help you solve this easily.

Generally speaking, you should add about 1 pound of substrate per gallon of water. This means that for a 5-gallon fish tank, a safe bet would be 5 pounds of gravel. Similarly, for a 20-gallon fish tank, roughly 20 pounds of gravel would suffice.

How Often Should You Change Gravel in a Fish Tank?

A very important part of adding gravel to a fish tank is the maintenance.

You don’t need to replace the gravel in your aquarium very often. Vacuuming your high-quality gravel particles should suffice.

Cheaper options tend to give up sooner, so make sure you purchase high-quality gravel.

It’s always better to add the gravel at the bottom of the tank before you set in the other decorations, add water and put the fish in.

Gravel can become floaty and won’t stay in place if you add it after filling the tank with water.

You should also make sure that the food particles don’t sink to the bottom of the aquarium.

The food accumulates within the gravel and starts rotting, causing it to produce hydrogen sulfite, which is a highly toxic substance for fish.

Remember that gravel is important for your aquarium or fish tank, so take all the above-mentioned factors into consideration before determining the quantity of gravel for your aquarium.

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