For a passive biofilter to work, aerobic conditions must be met for beneficial bacteria. The concept is to provide a medium for beneficial bacteria to grow in aerobic conditions. Here are numerous nonmechanical subsystem and passive biofilter projects:
Put a synthetic screen or scrub pad over a net pot, and this cannot be a material that holds much water or that is easily decomposable. Fill it with sand, gravel, ceramic material, charcoal or any porous substrate of choice, while pushing it inside the net pot. Sand helps remove small particles. This works to remove small particles if water passes from the top.
Ground layer biofilter
Gravel in the bottom of the tank will assist with biofiltration. It will help clear up the water.
Plants and microorganisms remove fish byproduct waste that is dangerous to aquatic animals. Fish provide properly balanced nutrients necessary for plant growth. Different types of aerobic bacteria complete the symbiotic cycle by providing the proper nutrient fixations and reduction of toxins.