I have always found that nature tends to take care of itself if provided the right materials. I think this is doubly so when you have an ecosystem that is able to run by itself.
The idea of a self-sustained aquatic system, where the waste of one organism is broken down and used as food for the other organisms which provide nutrients and food for other organisms in a constant ever-looping cycle has always fascinated me. I have tried to replicate this idea of a closed loop ecosystem as much as possible in my aquariums.
The main parts of this aquatic system are:
The soil and microorganisms in the soil:
This part breaks down nitrites and nitrates from larger organism waste and provide nutrients and a rooting system for the plants (a small Winogradsky column will form in a natural aquatic soil setting)
This part provides a filtering system for the water and removes CO2 buildup in the water while providing oxygen to the larger organisms. depending on additional equipment, such as a CO2 tank, these large plants can also deter growth of algae on the aquarium glass and environment.
This part can vary quite largely, but the main idea to keep in mind here is Bio-load. Bio-load refers to the amount of waste buildup that needs to be broken down and repurposed as nutrients for other parts of the ecosystem. A general rule of thumb is that a higher Bio-load leads to more effort to keep an ecosystem in check. Likewise, larger organisms have larger Bio-loads.
Macro-organisms can be as small and versatile as freshwater shrimp or crawdads (LOW Bio-load) or bigger organisms such as small fish or small frogs (MEDIUM Bio-load), or bigger Bio-loads, such as predatory fish (HIGH Bio-load).
Additionally, the more macro-organisms that are in the system, the larger the Bio-load.
this is not normal aquarium light, but actual sunlight (for small amounts throughout the day, or artificial grow lights that can replicate the requirements needed for plants to grow indoors.