Many aquarists worry that deep substrates can cause issues. Thick substrates can trap organic matter, leading to anaerobic (oxygen-poor) conditions where harmful bacteria thrive. However, not all anaerobic bacteria are harmful; some actually help convert iron into a form that plants can absorb more easily.
Despite this, it’s important to avoid excessive anaerobic bacteria. Thin inert substrates aren’t ideal for plant growth either. In contrast, thick layers of aquasoil provide a nutrient-rich environment and beneficial conditions for plant growth.
What is Aquasoil? We recommend aquasoil for plant growth, as it binds ammonia and stores nutrients. Aquasoil doesn't compact easily, even in deep layers, which helps prevent the formation of anaerobic zones.
Another Option? Aquasoil can be expensive, especially when deep layers are required. A more affordable alternative is using inert material, such as small lava rocks (3-5 mm), as a base layer, with aquasoil on top. Lava rocks are cheap, lightweight, and long-lasting. Other options include using garden soil with aquasoil on top, making maintenance easier.
What Should You Avoid? Avoid rocks like limestone, which can increase water hardness. Also, avoid using garden soil with high organic content in deep layers, as it decomposes in anaerobic conditions. Fine sand should also not be used in deep layers, as it traps organic debris, which can decompose and cause problems when the substrate is disturbed.
Conclusion: You can safely use deep layers of aquasoil. Lava rocks are an excellent choice for a base layer, but be cautious of organic material that may decompose in anaerobic conditions.