NOVELTY - Conditioning water in a contained aquatic environment comprises flowing an amount of water from the contained environment to a first apparatus for substantially reducing the oxygen concentration of the water, flowing the water to a second apparatus containing anaerobic bacteria to substantially reduce the nitrate concentration in the water, and flowing the water back to the contained environment.    USE - For conditioning water (claimed) e.g. fresh water, brackish water and salt water in aquariums and similar environments for holding fish, invertebrates, mammals, and other aquatic creatures, including coral and in other applications where toxic nitrates must be removed from water e.g. the aquatic farms, livestock farms, sewage treatment, purification of drinking water and industrial waste water treatment.    ADVANTAGE - The methods and systems maintains a healthy and efficient aerobic bacteria culture, ensures that a sufficient food supply is maintained for the bacteria culture, efficiently reduces nitrates to acceptable levels, controls the pH within safe levels, adds healthy minerals to the water, and reduces odors caused by the production of hydrogen sulfide gas formed in the autotrophic denitration process. The systems are light in weight relative to the size of the aquarium or similar closed environment of water, are easy to use, need little maintenance, and are unlikely to clog or overflow. The added negative ions into the aquatic systems are absorbed in the bloodstream of the aquatic life, and help the animals process the food more efficiently. As a result, the animals need less food to remain healthy, and improved health leads to faster growth. The anolyte also serves as a very powerful disinfectant against bacteria, viruses, and algae. The catholyte solutions also promote the health and growth of organisms used in the treating processes. As a result, the water is processed more efficiently, which can reduce the number of filters necessary to achieve the desired effect in the aquatic systems. The methods and systems uses devices designed to minimize water loss during the filtration process such that little or no water needs to be added to the enclosed environment. Less support media for the anaerobic bacteria is needed to remove the desired amount of nitrates than if the aerobic process was not used. This allows for a smaller, and significantly lighter weight, denitration chamber for the process, since the sulfur media used in the chamber can be relatively heavy. Additionally, the reduction in the level of dissolved oxygen in the chamber helps to prevent the proliferation of certain undesirable sulfate reducing bacteria, which are known to be filamentous, creating a thick, slimy coating on the sulfur media, which could cause the chamber containing the sulfur media to clog. The carbon dioxide produced by the aerobic bacteria allows the bacteria in the denitration chamber to remove nitrates more efficiently. Adding the calcium in multiple steps has the benefit of allowing the calcium source to be arranged to give long life with a minimum amount of clogging. This will result in increased life of the calcium media in the system because the acidity of the water is reduced when it contacts the less soluble calcium sources, so that the water having a reduced acid content will dissolve the more soluble calcium media at a slower rate. The degassing step reduces odorous gases, such as hydrogen sulfide gas, and other undesirable contaminants, which may be emitted from the biological processes occurring within the chambers. degassing can also be useful for raising the pH of the water by reducing carbon dioxide levels. The support media made of plastic is lightweight and may float in the aquarium water. Also it does not clog easily, and provides a large surface area for bacterial colonization.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a system for conditioning water in contained environment for holding aquatic life;    (2) an oxytower;    (3) a protein skimmer for removing contaminants from water;    (4) a mixing eductor;    (5) a desulfator for reducing sulfate concentrations in water;    (6) an aerobic bacteria chamber for reducing the concentration of oxygen in water; and    (7) a bio-filter for reducing ammonia to nitrite and nitrite to nitrate.