Understanding Filtration - pt.4
Natural Systems
The use of a natural system in an aquarium represents a full circle approach to fish keeping. Instead of trying to filter the water with various engineered filters and media, this method utilizes natural cycles to ensure high water quality. The use of plants in fresh water and live rock and sand in salt water are how this is accomplished.
In freshwater, plants can act as a filter by taking up nitrogen-based compounds like ammonia as a source of food. In aquaria if the quantity of plants is high compared to the number of fish, little else is needed to perform efficient filtration in the tank. Utilization of water pumps to circulate water around the tank to bring food to and take wastes away from plants is necessary for efficient operation. Carbon dioxide injection can also be used to enhance the growth of plants and further the filtration process. A thick layer of gravel (2-4”) may be necessary to help the plants establish roots and grow in health. To properly maintain the plants, adequate lighting must be provided to help them grow.
Systems such as these are referred to by the Europeans as aquatic gardens. A special note to be added is that these aquatic gardens are not intended to keep huge populations of fish, but just enough to “accent” the aquatic garden. Due to the large amount of plants, and the night time biology of plants using an enormous amount of oxygen, it would not support a vast amount of fish.
In saltwater, live rock can be used to filter the water. The end results are similar to the natural approach to freshwater, but the mechanisms are completely different. The rock that makes up “live rock” is not actually living, but it provides a mini environment for a multitude of life forms. Bacteria, protozoans, crustaceans, worms, mollusks, echinoderms, corals and sponges all make their homes in and throughout live rock. All of these along with zooplankton and phytoplankton (which are the beginnings of the food chain in the ocean) play important roles in a natural tank in that they add diversity and stability to the aquarium. The bacteria, are the most important, however, as they are the ones doing the bulk of the filtration. These bacteria are similar if not the same as the ones we encourage to grow in our biological filters to consume ammonia and release nitrates as an end product.
This process occurs essentially the same on live rock, but with an important difference. Deep within the rock, there are chambers connected to the outside buy minute fissures and cracks. Water works its way in and out of these cracks very slowly, so that in the interior low oxygen levels abound. Specialized bacteria that thrive in anoxic conditions preside here. These bacteria actually consume nitrates in the same manner as aerobic bacteria consume the ammonia. The end product created by these anaerobic bacteria is nitrogen gas—this bubbles up and out of the aquarium. The result of all of this is that wastes produced by inhabitants of the tank are reduced dramatically by the live rock. This lends incredible stability to the system and allows for high efficiency and long term maintainability, just as it works in the ocean itself.
For this approach to work well, it is important to have good circulation around the rock being used. Often the flow is not adequate and the system stagnates, and the bacteria have nothing to neither bring them food nor sweep away wastes. Utilizing a protein skimmer in conjunction with the live rock creates a very efficient system, requiring low maintenance. The skimmer removes proteins from the water before they break down into ammonia, reducing acid production and load on the filter.
Protein Skimmers
Protein skimmers are perhaps one of the most influential developments in keeping saltwater aquariums. They have made it possible to maintain very high levels of water quality for extended periods of time. Protein skimming may also be known as foam fractionation, and the concept behind it has been in use for decades.
Protein skimmers function in a deceptively simple manner. Foam is created by mixing dense saltwater (doesn’t work with freshwater) and air together – the finer the mix the smaller the bubbles, the more efficient the skimmer will work. Proteins and other organic molecules stick to the bubbles, which creates a stable foam that rises above the mixing air and water. This foam is then collected before it is returned to the tank.
The wastes, organics, and proteins that are collected are pulled out before they have a chance to break down into ammonia. This effectively scrubs the water clean, removing all manner of waste materials from the aquarium and making the biological filter more efficient.
Skimmers do need to be monitored regularly to make sure they are performing well, and not just taking up space and energy. Additionally, because they are so efficient at extracting proteins from the water, they sometimes pull beneficial material like organic molecules that corals use for nutrition and plankton that filter feeders consume. This underscores the need to perform regular water changes, to re-supply the tank with proper nutrients, buffers and salts to make sure all the animals are properly cared for.
UV Sterilizers
Ultraviolet sterilizers work by passing water through a sealed tube with an ultraviolet light; the light emits rays that sterilize or alter the DNA of living organisms that pass by it. Because this is fed by a pump with a pre-filter, large animals (like fish, etc.) are not harmed. Bacteria, protozoan, algae cells and parasites are all killed with this method. The key to using one of these is to size it correctly to the volume of water.
UV sterilizers are generally connected “in line” between the aquarium and the filter system. The UV light bulb is effective for about 6 months and then needs to be replaced.
