Mineralised top soil is a good medium in which to grow aquarium plants, because it breaks the down organic materials that contribute to unwanted algae growth in the tank. By exposing the soil microbes, enzymes and various bacteria strains to oxygen and water, organic matter in the soil is converted into bio-available minerals. Aquatic plants use these minerals to grow and reproduce. Clay provides iron and binds the soil. Dolomite adds magnesium and calcium to keep the soil from becoming too acidic and potash will supply a source of potassium.
Empty the topsoil into the plastic container and pour in sufficient water to completely cover the soil. Continue to add water until the level is a few centimetres above the soil. Continue to cover the aquarium bottom with this depth of topsoil.
Stir the top soil with your hand, to break up lumps and to ensure that the soil and water have mixed thoroughly.
Carefully pour off as much water as possible, after two days. Refill the container with water to its original level. Carefully pour off the water after another two day period.
Lay a large plastic sheet out in the sun and pour the moist top soil onto this. Spread out the soil as much as possible. Allow the soil to dry for at least two days.
Return the dry soil to the container and add water once again. Repeat this process at least three more times. Smell the dry soil. The soil will not smell once it is completely mineralised.
Submerge the soil under water once again and add the clay to it. Mix the clay thoroughly into the topsoil.
Sprinkle a handful of both the dolomite and potash on to the bottom glass of the aquarium. Add the soil and clay mixture to the aquarium to a depth of 2.5 cm (1 inch).
Place aquarium gravel of your choice on to the soil mixture. Add sufficient aquarium gravel to create a depth of 5 cm (2 inches) at the rear of the aquarium. Slope the gravel to create a depth of 2.5 cm (1 inch) along the front glass pane. Slowly fill the aquarium with water.