Aquarium Substrates

There are many different options for aquarium substrates and substrate is one of the most important components of a healthy tank.  Many fish interact with the substrate such as cory catfish who will swim along the bottom and rub up against the substrate or the many cichlids who love to dig.

Substrate is used for anchorage of fake plants and many aquarium decorations and as the medium in which live plants live and get their nutrients.  Substrate also provides a large surface area for healthy bacterial growth and it also contributes as mechanical filtration for undergravel filters.


Gravel is the most common substrate.  It comes in many different sizes and colors.  Pea gravel is about ⅛” and is by far the most common substrate seen in aquariums.  It provides a nice medium between finer substrates and coarser substrates and offers a nice natural look to your tank.

Coarse gravel up to ½” can also be attractive.  It allows more than adequate flow for an undergravel filter.  However, the larger gaps tend to allow food to fall through and get trapped beyond where bottom feeders can reach.

Gravel also comes in many different colors.  You can find gravel in blue, red, orange, and many other colors including rainbow colors.  This gravel is is perfectly safe to fish and does not contain any harsh chemicals.  Keep in mind that colored gravel can detract from the attractiveness of the fish and plants.

If you are unsure of which type of gravel to select for your aquarium, we recommend you go with natural color pea gravel.

Daniel Ahlqvist (Own work) [CC BY 3.0]
>Daniel Ahlqvist (Own work) [CC BY 3.0]


Sand is another good option for your tank. Many aquarium fish come from natural habitats with sand like substrate. Sand is a perfect option for fish that like to dig or burrow such as cichlids and loaches. It’s very fine which makes it safer for fish to rub against and it comes with the added bonus of being extremely inexpensive.

Coral sand is made up of crushed coral.  It looks the same as typical sand, but imparts the minerals that contribute to making the water hard and basic (pH being about 8).  If you are putting together an African Cichlid tank, coral sand does a great job to replicate the natural water parameters in Lake Malawi and other lakes in the area.


Soil is a great option if you are planning on a having live plants in your aquarium (often called a planted tank). Soil brings with it many of the vitamins and minerals that are critical for healthy plant growth.  Additionally, once your plants “use up” the nutrients in the soil, it will easily accept new minerals from fertilizers and decaying fish food, fish waste, and any plant growth that has fallen to the substrate.

There are a handful of other substrates that wouldn’t be considered natural like glass beads, but are still safe and offer different aesthetic qualities to your tank.  While these can be difficult to find, it is worth mentioning that they can still be safe assuming they have been manufactured specifically for aquariums.

Neale Monks [CC-BY-SA-3.0]
Neale Monks [CC-BY-SA-3.0]

Adding substrate

You will need roughly 1-2 lbs of substrate per gallon of water.  This can vary depending on your aquarium size and shape, ie. regular vs long vs tall, rectangular vs bowfront, etc.

Aquarium substrate that you purchase online or from a pet store will come pre-washed which should have removed excess particles and any other unwanted elements.  However, during shipping and transport, substrate (gravel in particular) have a tendency to ship and break resulting in small particles that should be removed prior to adding the substrate to your aquarium. Therefore, before substrate is added to your aquarium, it should be thoroughly washed and rinsed.

Gravel can be easily rinsed with a hose and a strainer.  Remove the gravel from the bag and put it into the strainer. Spray it with a hose or a faucet until the water running from it is mostly clear.  Once it is clear, you can add it to a bucket or directly into your aquarium. Gravel can also be washed in the same way as sand and soil.

Sand, soil, and gravel can all be washed in a bucket.  Fill the bucket about a quarter of the way with the substrate.  Then fill the bucket with water until the point where it is several inches above the top of the substrate.  Slosh the bucket around and mix the substrate.  The water should become cloudy.  Dump the cloudy water out as best you can while keeping the substrate still in the bucket.  Repeat the process until the water is mostly clear.

Substrate should be added to your aquarium sloping back to front with the back about 4 inches thick and the front about 2 inches.  This accomplishes several things.  First, it adds depth to your aquarium, making it look bigger than it actually is.  Second, it serves your live plants well.  Shorter plants that are typically used in the foreground have shallower root systems and taller plants which are typically used in the background have deeper root systems.