Aquarium soil substrate differs from typical gravel aquarium substrate because it contains nutrients to promote aquatic plant growth. Aquarists who want a lush green landscape in their tanks need a substrate that can support plant life. However, many problems can occur when using regular garden soil and fertilizers, such as algae overgrowth. Mixing a soil that is rich with clay and low in algae-promoting fertilizers will keep your tank clean while promoting the growth of your plants.
Pour the topsoil into a container. Fill the container with water until the water level reaches 1 to 2 inches above the soil level. Break up or stir the soil so it becomes thoroughly saturated.
Allow the soil to soak in the water for 2 days. Drain the water, then repeat Step 1 by adding more clean water after draining. Let the soil soak for another two days, then drain.
Empty the wet soil onto a clean tarp, plastic sheet, plastic tablecloth, plastic painter’s drop cloth or a very large, wide container, then spread the soil into a thin layer. Allow the soil to air dry completely. Speed the drying time by placing the soil outdoors on a sunny and dry spring or summer day.
Repeat Steps 1 to 3 two more times to neutralize the fertilizers in the soil that will contribute to green, murky water and algae.
Sift the dry soil through a strainer to remove debris, and return the soil to the original container.
Add 1 part pottery clay to 10 parts of soil. Pour warm water into the container and mix the clay and soil together until a cake batter-like mud has formed.
Sprinkle a small dusting of muriate of potash, a fertilizer, on the bottom of the empty aquarium. Pour the muddy soil/clay mix into the bottom of the aquarium.
Cover the mud with a layer of gravel of your choice. Some common choices include pea gravel, river stone and aquarium sand.
Refill the aquarium with water, add your plants and replace your fish.