Substrates and Fertilizers for Your Planted Tank

When designing a planted tank, there are several practical factors to consider. Sources of nutrients for your fish and plants are a top priority or your environment won’t survive long. The overwhelming majority of planted aquariums utilize a substrate layer on the bottom of the tank. When designing your tank, consider the wide variety of options available for both the color and material of your substrate. 

It is important to spend time thinking through your substrate choices as they are much harder to replace once the tank has been set up. Your substrate needs will be a large factor when considering the nutritional needs of the plants and creatures in your tank. Substrates often contain plenty of nutrients to fuel your tank for several months, but regardless of your choice in substrates, you will eventually need to replenish the nutrients with fertilizers. 

What Are Substrates?

Substrates are defined as the surface on or in which plants, algae, or certain animals, such as barnacles or clams, live or grow. Substrates serve as a source of food or energy for an organism. When it comes to aquariums, the substrate refers to any loose material that makes up the bottom of your tank.

This layer of your tank has several functions, the most important being that it promotes a healthy habitat for your plants and fish. Substrates offer a site for beneficial bacteria to grow and help in breaking down waste by products of the fish. The color of your substrate can also be used to enhance the aesthetics of your tank.

The substrate you choose will serve a role in your tank’s nitrogen cycle. The right substrate will help bacteria grow and colonize. It also servers the physical purpose of providing a structure for rooted plants to grow around.

Choosing the right substrate material for your tank is essential for success, especially with rooted aquatic plants. There are plant-specific substrates that are infused with the nutrients needed for healthy plant growth. Some substrates can even balance the pH of the water which is helpful for very fickle plant species. Other substrates can be mixed with nutrient tablets to help maintain proper pH, alkalinity, and nutrient levels.

What Are Substrate Fertilizers?

Before you add your substrate material to your aquarium, it is recommended to put a layer of fertilizer on the very bottommost layer. Fertilizers at this layer are carriers for the nutrient material and provide the sustenance to the plants and fish. This is where bacterial growth flourishes in your tank.

If your tank is heavily planted, it is essential to have a substrate fertilizer layer. Aquatic plants use iron, magnesium, and potassium as well as other macro and micronutrients to grow and develop. Most types of plants in your tank will utilize the fertilizer as their primary nutrient source, which if done properly, should be an abundant source. Some plants feed primarily through their leaves, while others are root-feeders. Use an enriched plant substrate when setting up your aquarium for root feeders or insert fertilizer tablets around the roots on a regular basis. Any areas lacking nutrients can be made up for by adding fertilizer into the water column.

Substrate Materials

Substrates come in all types of materials and colors. Gravel is probably the most common substrate choice, especially for new aquarium owners. Gravel provides a solid bed for nutrients to be stored and allows certain fish to burrow and dig. Fish also love sand substrates for this reason. You may also see options for crushed coral which is a great solution for maintaining the pH balance of your water and certain fish thrive with this substrate.

While most substrates are natural materials such as stones, sand, and gravel, you may find some options for inorganic materials like marbles. While not quite a natural substrate, marbles are great for certain types of egg-scattering species of fish. You have probably seen this set up used for betta fish. Marbles are also great for easy maintenance.

If live plants are kept in the aquarium, it is common to use laterite or vermiculite as substrate. These materials can store and release important nutrients for the live plants. They are usually used as a lower layer of the substrate and covered with a layer of gravel.

Let’s take a look at the most common substrate material options.

Pebbles: These are one of the largest substrates available on the market. Pebbles can be made up of many different materials, from glass, colored plastic, quartz, etc. Pebble substrates are often chosen because the materials used do not have an impact on water quality. If you are a beginner aquarist, pebbles might not be your best choice. While they are aesthetically pleasing, pebbles can be problematic for rooted plants and the overall environment in your tank. Pebbles leave gaps in the substrate bed which can cause buildup of uneaten food and unprocessed fish waste. This looks bad and can cause a toxic environment for your plants and fish. 

Gravel: Gravel is basically a smaller version of pebbles but they don’t have the downsides of full-sized pebbles. Gravel also comes in a wide variety of materials and colors which allows you to fit your design tastes. Gravel is also able to be cleaned and maintained on a regular basis using what is known as a “gravel vacuum”. 

Sand: Aquarium sand is no different than the sand you find at the beach. Sand options range in grain and size and come in a variety of colors. Sand substrates are the most natural option and are the easiest to keep clean.

Soil: Unlike sand, aquarium soil is very different from what you find out in your backyard. Substrate soil is specially formulated to prevent it from mixing with water so you don’t end up with a tank of muddy water. Soil is very effective at providing nutrients to the plants in your tank and is not recommended if you don’t have any plants. 

Whatever substrate you choose for your planted tank, it should complement the aesthetics and provide a practical source of nutrients for the tank’s inhabitants.

Substrate Quantity

Once you have chosen your substrate material, it is important to know how to properly apply it to your tank bed. Most substrates use the 1-3-inch rule for depth, but some rooted plants will require a deeper bed for optimal growth. You will need to be careful not to crate too deep of a substrate bed as that can be problematic for certain fish and plants.

There is no limit to how much substrate you can use in your tank, but there are some things to keep in mind. Thicker substrates leave less room for decorations, plants and more fish. As with all parts of your aquarium, you will eventually need to perform cleaning and maintenance. The more substrate you have, the more you will have to clean. 

Substrate quantities can also vary in different areas of your tank. Some aquarists focus on creating a varied landscape inside the tank to be more visually appealing (this is known as aquascaping). 

Substrate Color

There are two very different types of aquarium owners when it comes to the color of your substrates. Some aquarists argue that regardless of the material, substrate colors should mimic or match colors of a natural underwater habitat. Other planted tank owners think substrates are a chance to express their personality or creativity. From neon gravel to glow-in-the-dark sand, there are options for the most enthusiastic aquarium owner. 

Substrate color ultimately doesn’t affect the health of the creatures in your tank. While the colors you choose may not be natural to the ocean, studies have shown that unnatural colors won’t harm your tank inhabitants. The overwhelming majority of fish are very adaptable and will thrive in a colorful environment as long as the water conditions are good.

Substrate Maintenance

Regardless of what substrate you choose for your tank, eventually it will require maintenance and cleaning. It is important to regularly remove any accumulated waste that finds its way into your substrate. There are specialized vacuums for certain substrates like gravel which will remove debris without removing the substrate. Consider doing substrate maintenance anytime you do a water chance in your tank.

Think of the Fish

Substrates serve to create a more natural looking and feeling habitat for fish. Substrates are particularly important for fish who are prone to burying eggs and digging for food. Substrates can also make aquatic life feel safer and at home by reducing reflections off the aquarium glass. Some fish scatter their eggs on the substrate layer in order to hide them from being eaten by other fish in your tank. The truth is while you don’t absolutely have to have a substrate layer. Bare-bottom tanks are available, but the benefits of a substrate layer far outweigh the negatives. A properly chosen substrate layer will lead to a healthier overall aquatic environment for your fish and your plants.