How Much Substrate per Gallon Should You Use in Your Tank?

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If you’re a newbie to the fish-keeping hobby, you’ll be keen to provide the perfect environment for your new pets.

Once you’ve chosen your aquarium and decorations, you’ll need something to cover the tank bottom.

But how much substrate do you need to use per gallon of water? And with so many high-quality substrates to choose from, how do you pick the best one for your setup?

Read this guide to learn how much substrate per gallon you need for your fish tank and more!

How Much Substrate per Gallon?

The general rule of thumb for the ideal depth of an aquarium substrate is 1 to 3 inches of substrate.

That depth means that your live aquarium plants have plenty of room to anchor themselves and spread their roots, and beneficial bacteria have sufficient space to grow.

Although there’s no minimum or maximum when it comes to the depth of your substrate, do bear in mind that too many inches of gravel is not really necessary and does take space away from your livestock.

Minimum Substrate Depth

Ideally, you don’t want to have less than one inch of gravel or other types of substrate in your tank.

That substrate depth is probably fine in a tank without plants and for most fish species. However, if you want plants, you’ll need a couple of inches of substrate at least, and deeper-rooted species will need more than that.

Ideally, you should allow 1 to 3 inches of gravel or 1 to 3 pounds per gallon of water.

However, to get the depth absolutely right, do some research into the typical root size and spread and choose the amount of substrate to suit that.

Therefore, for a 10-gallon tank, you’ll need around 10 pounds of gravel to give you a 1-inch depth of substrate.

How Much Substrate Do I Need for a Saltwater Tank?

If you have a reef or a marine tank, you can use the same process to determine how many bags of gravel or sand you need.

So, decide how many inches of substrate depth you want and calculate the amount of sand or gravel accordingly.

For 1 inch of sand or gravel, you’ll need 1 pound of substrate for every gallon of water in your setup. For 2 inches of substrate, you should allow 2 pounds of a substrate, etc.


The depth of substrate you decide to use depends to some extent on the type of look you want for your tank and what you intend to keep in it.

Some people opt to go for a minimalist look with no substrate at all. However, I think that can cause problems with reflections and glare that could frighten and stress your fish.

Generally, it’s best to choose a type and depth of substrate that reflects conditions in the fish’s natural environment.


Gravel substrate comes in a variety of colors, which makes this kind of substrate very popular with kids.

A darker substrate can help to show off pale-colored fish and makes colors really pop, especially when teamed with imaginative planting. So, choose a substrate that suits your fish’s color so that they don’t blend in and get lost against a background of a similar color.

Keep It Natural

The fish and invertebrates you choose to keep will come from habitats where there is some kind of substrate, and many of the aquatic plants you can keep will need some sort of substrate in which to anchor their roots.

Without a suitable substrate in which to spread their roots, the plants will float away in the filter current, and some won’t survive since they derive most of their nutrients from within the substrate.

Beneficial Bacteria Colonies

Finally, the beneficial bacteria you want to grow in your tank to process ammonia, nitrites, and nitrates live on and in your aquarium substrate.

If you don’t have any form of substrate, the number of those bacteria will be much-reduced, potentially leading to an ammonia spike in your tank that could kill your fish.

Substrate Varieties

There are several different kinds of tank substrates to choose from, including the following:


Gravel is by far the most popular kind of tank substrate in the hobby!

Gravel is a relatively easy-to-clean substrate when you use an aquarium vacuum cleaner, and it comes in various sizes and colors to suit your fish and your aquascaping.

Generally, gravel can be from 2 to 5 mm in size and sometimes contains slightly larger pieces of rock.

Gravel is an excellent medium for tanks containing aquatic plants and provides plenty of space for beneficial bacteria colonies to grow and become established.

Smaller gauge gravel has the advantage that there’s less space between the stones where organic waste can become trapped. Tiny shrimp and fish are also less likely to get stuck within the substrate.


Although sand is more commonly used in saltwater marine or reef tanks, you can also use it in tropical and brackish setups.

Aquarium sand is a fine, dust-like particulate medium rather like mud and soil and most closely replicates what most fish species have in their natural habitat.

Sand doesn’t trap organic matter, which simply lies on top of the substrate, making it much easier to keep clean than gravel.

The main downside of using sand as a substrate is that it can stifle plant roots and tends to get sucked into the filter intake.


Pebbles can look beautiful in an aquarium. You can buy rock, resin, and quartz pebbles measuring anything from a few millimeters right up to around 50 or 60 mm.

Although using pebbles as a fish tank substrate is undoubtedly extremely very effective aesthetically, large gaps can form over time between each layer of pebbles, trapping detritus.

In addition, smaller fish and shrimp can also become trapped.


Aquarium soil is generally used by aquarists who want to grow plants in their tanks. This kind of soil is not like the kind you have in your garden. Aquarium soil usually contains a mixture of the correct nutrients your fish need to thrive and grow.

Never take soil straight from your backyard and put it into your fish tank!

That can be extremely dangerous to your fish since it potentially contains chemicals, fungi, bacteria, and other harmful critters that you don’t want in your tank.

What’s the Best Kind of Substrate for My Aquarium?

how much substrate per gallon

There are several factors that will help you decide what kind of substrate is best for your aquarium.

Aquarium Size

First of all, you need to consider your aquarium size.

When deciding how many bags of substrate you need for your tank, you’ll need to consider that bags of substrate come in different sizes and volumes. Obviously, the larger your fish tank, the more substrate you will need.

In a large aquarium, you can even get creative by using layers of different substrates. If you want to use lots of aquatic plants, you can use aquarium soil as a base layer to provide the plants with nutrients and then add gravel or sand on top.

Livestock Types

The type of fish and other aquatic life you keep will, to some extent, dictate the kind of substrate you use.

For example, if you have bottom-dwelling species, a very coarse gravel might not be the best choice, as that could injure your fish. Shrimp and very small fish could become trapped in the gaps between pebbles or very large gravel pieces.

If you keep goldfish or cichlids that like to dig and root around in the substrate for scraps, you’ll probably find that an additional inch or so of gravel will help to keep your plants securely in place.

So, if you think carefully about the creatures you want to keep in your tank and choose a substrate that most closely replicates that of their wild environment, you won’t go far wrong.

Filtration System

The filter system you run will also dictate the kind of substrate you can use.

For example, if you choose an undergravel filter, you’ll obviously need to choose a gravel substrate that allows fish waste to drop through the pieces of gravel onto the filter plate.

However, if you have sand as your chosen substrate, you’re better off choosing an external filter so that the sand doesn’t get dragged into the filter box and clog the impeller.

Aquatic Plants

If you want to use living aquatic plants in your aquarium, you need to consider their requirements carefully. That will enable you to choose the correct composition and depth of the substrate the plants need for optimum growth and health.

For example, some plants, such as Moneywort and Anubias, don’t grow well in sand, preferring gravel or soil in which to root and grow.

However, if you choose plant species that derive most of the nutrients they need from the water column, the substrate type is not as crucial.

Finally, plants need essential nutrients such as potassium, magnesium, and nitrogen to thrive, and some types of soil or gravel might not provide the plants with what they need.

So, you’ll need to supplement that with root tabs or liquid fertilizer.

Final Thoughts

I hope you enjoyed our guide to how much substrate per gallon you’ll need for your freshwater or saltwater fish tank. If you did, please take a moment to share the article.

The depth of substrate you need depends on a number of factors, including whether you’re intending to keep rooted plants, the size of your aquarium, and the livestock species you intend to keep.

You can work out how much substrate per gallon you’ll need by using a simple calculation.

For a 10-gallon tank, you’ll need around 10 pounds of gravel to give you a 1-inch depth of substrate. Simply multiply that according to your aquarium size.

What depth of substrate do you prefer for your fish tank? Tell us in the comments box below!

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