Dedicated aquatic plant hobbyists have always searched for new and improved ways of maintaining vibrant freshwater flora. While the so-called, ‘dirted tank’ method is far from new, it continues to create excitement in the aquarium hobby. While many methods of creating vibrant planted aquaria exist, few of them rival the simplicity of a ‘dirted tank’. Using topsoil or potting soil as a substrate is not a new idea and aquarists have been using this method to grow healthy aquatic plants for decades. As the hobby has progressed, so has our understanding of the requirements of freshwater plants. The following article will seek to provide a detailed, step by step, guide on how to setup a ‘dirted tank.’
- Cheap topsoil
- Dolomite Lime
- Sulphate of Potash (Potassium sulphate)
- Blood and Bone
- Gravel or sand
- Large container for soaking soil
- Old Fish Net
Step 1 – Purchase and Rinse the Topsoil
Finding a suitable soil proved to be the hardest part of this project. Most hobbyists outside of Australia use Miracle Grow Organic Choice Potting Mix, however, at the time of starting this project, Miracle Grow was unavailable in the local area. Most other brands on the market contain synthetic ingredients, such as; wetting agents and inorganic fertilisers. These ingredients are undesirable and can cause problems if added to the aquarium. Eventually I found some cheap topsoil at a local garden supplies centre. The topsoil was not branded but was of a suitable consistency and was 100% organic, without any added fertilisers.
Once you have found a suitable topsoil, open the bag and distribute it in the container of your choice for soaking purposes. I used a wheelbarrow for this purpose. Fill the container with water so the water level is a few inches above the top of the soil. Stir the topsoil to break-up any clumps. This will also cause any bark to float to the surface. Remove any floating debris with an old fish net. Let the soil soak for a day or two. Come back and slowly dump the water off of the top. Any floating bark that remains will be poured off with the water. Now add in more water so the soil is well covered. This water changing process helps to “rinse” the soil of any possible fertilisers or other harmful water soluble chemicals. Stir the soil repeatedly, removing any debris which floats to the surface. Repeat this process until no bark/debris remains.
As I live in a cold climate, I was unable to ‘mineralize’ the soil during the process. Mineralization involves wetting the soil, letting the soil dry and then soaking it again. This process is repeated several times until the soil loses its ‘earthy’ smell. Obviously this requires a warm climate. The warm and moist environment created by the wet soil provides the perfect environment for bacteria to grow. The bacteria break down the organic matter in the soil into humic substances. The humic substances become a readily available source of dissolved organic carbon (DOC) for the plants later on. On top of this, when the water evaporates from the soil, it leaves behind mineral ions. These mineral ions can also be utilised by aquarium plants. This is where the term, ‘mineralization’ comes from.
Step 2 – Create an Aesthetic border
Add the gravel/sand of your choice along the front and side edges of the aquarium bottom. Wet it just enough that it holds a slope and press it up against the sides. Doing this step ensures that the soil layer cannot be seen when viewing the tank from the front and sides. In this instance I have chosen to use 1mm black sand as a substrate top layer. The dark colour of the substrate will conceal any dirt that may rise to the surface later on.
Step 3 – Add the Dolomite Lime, Sulphate of Potash and Blood & Bone
Sprinkle each of the above on the bottom of the aquarium, so that it forms a thin layer across the bottom. For this build I used; 20mL Dolomite Lime, 30mL Sulphate of Potash and 40mL Blood & Bone. The Dolomite Lime contains CaCO3 which raises the pH of the soil and prevents over acidification of the soil, which can be detrimental to plant roots. The Sulphate of Potash and Blood & Bone add Nitrogen, Phosphorus and Potassium (NPK) to the soil. These are the three essential macro-nutrients required by plants.
Step 4 – Add the topsoil
Fill in the borders you’ve created with the mud. This layer should be anywhere between 2.5cm and 5cm thick. As I used a fine sand, I chose to use a 2.5cm thick layer of mud. The thinner layer prevents anoxic environments from forming in which harmful anaerobic bacteria can multiply.
Step 5 – Top with Sand/Gravel
Cover the mud with the same sand/gravel that you used in step 2. This layer should be anywhere between 2.5cm and 5cm. The coarser the sand/gravel you used, the thicker this layer can be. I chose to use a 2.5cm thick layer in order to avoid anaerobic pockets.
Step 6 – Slowly Fill the Aquarium and Begin Planting
Begin planting and filling the aquarium as you would any other planted aquarium. Use caution when filling the tank with water, so as to avoid disturbing the substrate and uncovering the soil.