How Much Substrate Per Gallon Of Aquarium Tank? (2024 Guide)

Dr. Mollie Newton
Published by Dr. Mollie Newton PHD| Senior Editor
Last updated: May 8, 2024
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When looking to construct the ideal environment for our aquarium, it is crucial to contemplate various necessary elements.

Along with the fish you’ll be caring for, the plants and decorations, the substrate on the bottom of the tank itself plays a key role in the overall health of your new aquarium.

Whether looking to use sand or gravel, there are lots of different ways to modify your tank so that it meets your specific needs.

If you’ve ever asked the question “how much substrate per gallon,” read on for the answer to this and many other common concerns when setting up a tank for the first time.

Article Summary

  • Aquarium substrate is the material used at the bottom of an aquarium, and it can be sand, gravel, or soil, chosen based on the aquarium’s theme and purpose.
  • A general guideline is to use 1 pound of substrate per gallon of water volume in the aquarium.
  • For planted tanks, 1-3 inches of substrate or 1-3 pounds per gallon are recommended.

What Is Aquarium Substrate?

Nano Aquarium
Nano Aquarium

Generally speaking, aquarium substrate is whatever substance, be it sand, gravel or soil, that you decide to use on the bottom of your tank.

Which one you choose for your aquarium depends largely on what your goals are for the overall theme of the tank.

While brightly colored pebbles and stones may look pretty, they may not always be the best way to go.

Selecting a Substrate

For example, if choosing to go for a heavily planted tank with lots of hardy rooted plants, a gravel-only substrate may not be the best way to go.

This is because gravel, unlike soil, may not provide the adequate nutrient base or structure that plants need in order to root down and be healthy.

Why Do Aquariums Need A Substrate?

Along with providing additional aesthetic value separate from just having a glass-bottom tank, gravel substrates can serve a variety of purposes for the fish and plants in the aquarium.


Gravel and other substrate can increase the overall amount of nutrients, create an additional layer of insulation, and help fine tune your filtration with the aid of beneficial bacteria.


Substrates such as a layer of gravel also provide your plant friends with a place to stabilize and root down.

Without some gravel to hold them in place, planted tanks would just have a bunch of floating plant material all over the water column!


The nitrogen-fixing bacteria living on the surface of gravel play a critical role in keeping ammonia levels from rising in the tank, preventing ammonia poisoning and toxic shock that can cripple or even kill your fish.

Types of Substrate

There are a wide variety of substrates that one can layer on the bottom of the tank.

The one you choose is largely up to the determining factors of your specific tank, and some of the most commonly used ones in the fish tank are:


While not an exact measurement, pebbles range in size from a few millimeters up to around 60mm.

Pebbles can come from a plethora of different sources. Some can be rock, quartz, or even plastic!

These can make for a colorful, varietal substrate but the difficulty comes in the large gaps that form over time between a layer of pebbles.


These gaps can be dangerous because they can trap material coming to rest on the surface of the substrate. This includes fish waste, discarded food and bits of live plants, which can slowly decay over time and 


Aquarium with Gravel Substrate
Aquarium with Gravel Substrate

Compared to pebbles, gravel includes smaller bits of rocks larger that vary from 2 to 5mm in size.

This smaller size comes with the advantage that they have much less space between each layer, meaning less room for things to get trapped.

Gravel can be a great choice for the beginner aquarium, as it’s easy to keep clean.


Think of the classical beach sand that we all know and love, and that’s what most aquarium sand is!

As a fine, dust-like particulate, sand is often considered one of the more natural of substrate materials along with mud and soil, as this is what most fish you’ll see in an aquarium have as substrate in their natural environment.

Being even finer than gravel, sand has the added benefit of even less space for particles such as fish food and wastes to get trapped, meaning less cleaning and less worry about ammonia buildup.


Unlike your typical bag potting soil, the kind meant for aquariums is formulated a bit differently. As it’s meant to avoid mixing in with the main body of the water, using dissolved chemicals to achieve this.

As a general rule, stick to soil or gravel substrate that is meant for the home aquarium! Premade soil comes with the proper mix of nutrients to ensure healthy growth.

Along with being a generally poor idea for placement in the aquarium, soils and gravel pulled straight from the garden can be potentially dangerous to the health of fish and plants in the tank.

Bacteria, fungi, and other unhealthy critters can hitch a ride into your aquarium if you try to go the easy way.

Choosing The Right Substrate For Your Aquarium

Aquarium with Mixed Substrate
Aquarium with Mixed Substrate

It would be great if we could simply pick the gravel substrate that we like the look of for our aquarium and call it a day, but unfortunately that’s not the best way to design a tank!

When it comes to choosing your grave; substrate for fish tanks, we need to consider the plants and fish that will be calling the new aquarium home and design accordingly to best suit their needs.

Some important tank factors to consider when choosing substrate include…

Tank Size

When deciding how many bags of gravel or other substrate are necessary for your fish tank, the fact that they come in many different volumes is an important consideration.

A larger fish tank with more depth will obviously need much more substrate than a shallow fish bowl, and has room to get creative with a single layer or more.

A larger aquarium means more room to layer different substrates. If you’d like, you can use soil as a base to provide the most nutrients to your plants with gravel or sand on top to benefit your fish!

Substrate Depth

How much gravel/sand to use in an aquarium

When it comes to depth of substrate, a minimum inch measurement of 1-3 inches of gravel or substrate is best.

This ensures that your live plants have a good amount of room to root down and that beneficial bacteria have adequate room to form.

There is no inch minimum when it comes to substrate depth, but keep in mind that it does take space in the tank away from your fish!

Fish Species

The types of fish you’re keeping in the aquarium play a significant role in substrate selection.

Certain bottom dwelling species, like the tiger shovelnose catfish, may not thrive with excessively coarse gravel, as it can pose a risk of potential injuries.

Others fish may in turn like a more fine gravel that they can dig around in. 


Consult with the breeder, pet store, and guidebooks for information on the specifics of what kind of gravel or other substrate works best for the fish in your tank.

Considering that it will be their full-time home, it’s important to get things as comfortable as possible.


Adequate filtration is a must whether planning on soil, sand, or gravel substrate.

Once you determine the filtration needs of your fish tank, consider the use of an undergravel filter if using gravel as a substrate to bolster the natural biological filtration provided by the bacteria on the substrate.


When creating a planted aquarium, you need to look at the requirements of the plants when trying to determine things like depth and composition of substrate.

For example many rooted plants such as L. repens, moneywort and anubias will have difficulty growing in sand, and need something more like gravel or soil in their tanks to thrive.

Nutrient Content

When selecting gravel for your plants, look at the nutrient content.

Key nutrients such as magnesium, potassium, and nitrogen figure in major ways to the life cycle of the plant, and some gravel or soils may not be right for the plants in your fish aquarium. Planted tanks have the extra beauty of the rooted plants, at the cost of needing appropriate substrate to keep them healthy.


While a thick, dense substrate of several inches or more may look out of place in a small aquarium, you can adjust the surface to create whatever effect you desire.

Using a post or your hand, you can make valleys and troughs within the substrate in order to create more of an interesting looking texture.


Aquarium with Decorations
Aquarium with Decorations

Feel free to use gravel to augment the decorations already in your fish tank.

Having some rocks or gravel can give an authentic look to your aquarium that really suits some aesthetics, after all the point is that you’ll be looking at your aquarium, after all!


Be sure to wash any decorations before adding them to your aquarium, as some may come with a protective coating that can be harmful to your fish.

How Much Substrate Per Gallon

As a general rule of thumb, a good guideline is to aim for 1 pound of substrate per gallon of water volume in your fish tank.

This applies for any kind of substrate, whether sand or gravel!

When looking at how many pounds and bags of gravel or other substrate to use, it’s good to factor in that you’ll likely want to buy more than you need, just to be safe.

Substrate Calculator

Using an online substrate calculator can be a great way to determine the amount of gravel you’ll need in your aquarium, and some even factor in the cost for you!


Using a substrate calculator is no substitute for proper knowledge, and we recommend doing your research on all of the appropriate factors before putting substrate or decorations in your aquarium.

How Deep Should Fish Tank Substrate Be?

A minimum of one inch of gravel or other substrate is the recommended lowest to go with, up to as many inches as you feel is appropriate.

When trying to keep plants in your aquarium, keep in mind that the inches of substrate is dependent on their roots. Deeper rooted aquarium plants will obviously need more gravel and soil to dig into in order to feed properly. 

How Much Substrate Per Gallon Planted Tank

When looking at an aquarium with live plants, again the recommendation is a minimum of 1-3 inches of substrate or 1-3 pounds for every gallon of water.

Figure out the maximum root size of the plant if trying to be exact, and suit the amount of substrate that you add accordingly. A 10 gallon tank would therefore need 10 pounds of gravel to reach an inch of substrate.

How Much Substrate Per Gallon Saltwater Tank

Saltwater Tank with Gravel Substrate
Saltwater Tank with Gravel Substrate

In trying to determine how many bags of gravel you’ll need for a saltwater aquarium, the process is much the same as a freshwater tank.

Consider how many inches in depth of substrate that you’d like, and plan the amount of gravel accordingly.

  • For 1 inch of gravel, plan on 1 pound of gravel for every gallon of water in the tank.
  • For 2 inches of gravel, 2 pounds of gravel for every gallon in the tank, and so on and so forth.


To get to an inch of gravel substrate in a 10 gal tank, you’ll need the same 10 pounds of gravel you would in freshwater.


Throughout today’s post, we’ve looked at answering how much substrate per gallon is appropriate for the home aquarium.

We’ve also discussed the different varieties of substrate that you may choose, such as soil, sand, or gravel, and their uses.

Our advice is to aim for a minimum of 1 inch of substrate on the tank, and a good rule to go by is using one pound of substrate per gallon in your tank.

Feel Free To Share!

As always we hope that you’ve enjoyed today’s article on gravel substrates and that it has answered whatever questions you may have.

Feel free to share this information with any other fish fanatics in your life, and don’t forget to check the site for more guides and reviews.

We wish you the best of luck on your aquarium adventures!

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