BioVivara

First, let’s define active and passive systems. A system, in this context, is the collection of fundamentals, like air and water, that make up a vivarium and its ecosystem. These systems can be managed passively or actively.
The Passive System

A passive system relies on the natural flow of air or water. For example, in a passive system a vivarium owner would rely on gravity to pull water through the substrate. Most vivariums today employ passive air flow systems that rely on a series of vents and/or screens to ventilate the air. As the air warms, it cycles through the vents and/or screens.
The problem with a passive system is the ecological balance of the vivarium is difficult to maintain because the normal systems found in nature (like moving air and water) are only minimally present. When passive systems are found in nature, like a stagnant pool, we find an overabundance of parasites, bad bacteria and disease. In a passively managed vivarium, toxic conditions can develop that kill plants and animals. For example, CO2 can build up and suffocate small animals, such as dart frogs. Bacteria, fungus and parasites can grow out of control, destroying plants and infecting the other vivarium inhabitants to the point of death.
Though not all passive systems will immediately have problems, when a vivarium suddenly “crashes” (plants and/or animals suddenly die off) it is often a result of mismanaged systems that did not promote a healthy, sustainable ecosystem. Something was “off” and it finally triggered the collapse of the vivarium’s environment.
The Active System

An active system is one where the ecosystem fundamentals are actively managed and controlled to create a balanced, healthy environment. For example, a fan is introduced to the vivarium to actively promote air movement, which keeps CO2 from building up and air from stagnating. Water is actively filtered and moved with a pump, helping to oxygenate the water and prevent bad bacteria build up. Humidity levels can be managed with an ultrasonic humidifier to suspend water into the air column.
Active systems do not necessarily require a lot of work. Once we know what must be managed, we can add the controls necessary to keep the vivarium’s ecosystem healthy. Timers and controllers can be implemented to automate system management.
It should be noted that, for the safety of our plants and animals, it is important to keep environmental controls out of the living space of the vivarium. We should never add moving parts and electrical components (like fans, lights, etc.) where they can be accessed by our pets.
Up Next: The Ideal Vivarium: Air Flow


Seth
http://www.biovivara.com