What Aquarium Substrate is Right For Your Fish Tank?

The substrate in a freshwater aquarium does more than look nice. Beneficial bacteria grow on it and help break down fish waste, and it anchors live plants and decorations.

Is it necessary to have substrate?

No, substrate isn't strictly required, and some fishkeepers prefer a bare-bottom tank. A bare tank is easier to clean because you simply siphon waste off the glass.

The trade-off is less surface area for beneficial bacteria. According to UF/IFAS Extension, aquariums need a biological filter where nitrifying bacteria can colonize, because those bacteria turn toxic ammonia into nitrite and then into the much less toxic nitrate.

Your filter can handle most of that work, but substrate adds extra surface. Waste is also more visible in a bare tank, and if you want rooted live plants, substrate is a must.

Is gravel or sand better for an aquarium?

It depends on the fish you keep, the look you want, your filter, and how you like to clean.

Gravel comes in many colors and sizes and hides waste between cleanings. If you want an undergravel filter, you need gravel, because water has to flow through the bed.

Some bottom-dwelling fish, such as loaches and corydoras catfish, sift the bottom for food. Sharp-edged gravel can injure their sensitive barbels.

Most aquarium gravel is inert and doesn't change pH. Gravel or sand made from calcium carbonate, such as crushed coral or aragonite, raises pH and hardness, which suits some fish but not others.

If you keep bottom feeders on gravel, choose small, smooth gravel. Larger gravel suits larger fish.

Sand looks more natural, and burrowing fish such as some loaches turn it over as they forage.

The downside is that waste sits on top of sand and shows quickly, so sand tanks need regular cleaning. Avoid fish that produce a lot of waste in a sand tank unless you're ready for frequent maintenance.

Deep, compacted sand can develop pockets with no oxygen, where decaying waste can produce toxic hydrogen sulfide gas (it smells like rotten eggs). Keep sand fairly shallow, stir it gently, and vacuum the surface during water changes to prevent this.

What is the best aquarium substrate for plants?

Plants feed in different ways. Some take most of their nutrients from the water, and others, called root feeders, draw nutrients from the substrate.

For root-feeding plants, many aquarists use a nutrient-rich plant substrate such as the Fluval Plant and Shrimp Stratum. Others put a layer of aquarium soil under the gravel.

Keep in mind that the nutrients eventually run out. Over time you'll need to add root tabs or other fertilizer.

Very fine sand can compact around roots, which some plants dislike. A coarser sand or fine gravel usually works better for rooted plants.

Types of Aquarium Substrate:

Pea gravel

Comes in many sizes and colors that can be combined for an interesting look. Its open structure lets water flow through the bed. Check that it's inert, since some natural gravels contain limestone that raises pH.

Quartz gravel

An inert material widely used in aquariums. It works well for rooted plants when paired with root fertilizer.

Silver Sand

Fine, inert sand. Rinse it well before use to keep the water from clouding.

Lime-free gravel

An inert gravel that won't change your water chemistry, which makes it a safe choice for most freshwater tanks.

Alfagrog

A porous, inert ceramic with a large surface area. The large surface area gives beneficial bacteria plenty of room to grow.

What additives should I use with substrate?

Most plain substrates contain no plant nutrients, so you need to add them. Some plant substrates come with nutrients already included.

Laterite is a common additive for substrates without nutrients. It's an iron-rich clay that helps feed plant roots. Mix it into the bottom layer of the substrate before adding water.

How deep should the substrate be in a planted aquarium?

A planted gravel bed is often about 2 to 3 inches deep. Slope it so it's a little deeper in the back than in the front.

How do you clean sand in a fish tank?

Hold a gravel vacuum just above the sand so it lifts waste off the surface without sucking up the sand. Gently stirring the top layer first helps loosen trapped debris.

How much sand should you put in your aquarium?

Keep sand shallow, about 1.5 to 2 inches for most tanks. A shallow bed is easier to clean and less likely to develop oxygen-free pockets.

What substrate goes with which fish?

For bottom feeders such as corydoras catfish and loaches, fine sand works best. Very small, smooth gravel can work too.

These fish forage through the substrate with their sensitive barbels, so avoid anything sharp. Sand-sifting cichlids such as Geophagus also do well on sand.

How do you slope substrate?

Make the substrate higher in the back than in the front. It looks better, and debris tends to collect toward the front, where it's easier to siphon out.

Sources

• Ammonia in Aquatic Systems, UF/IFAS Extension
• 4-H Marine Aquarium Project Book, UF/IFAS Extension