Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 131

Some other life support equipment may be found on aquarium systems or to treat incoming water.

Ion‐exchange filters are deionization units that can be used to treat incoming freshwater. These use two types of synthetic resins to remove positively charged ions (cations) such as calcium, magnesium, and sodium, and negatively charged ions (anions) such as chloride, sulfate, and bicarbonate. In addition to conventional deionization, ion‐exchange filters can contain resins or adsorbent media that are selective for specific contaminants such as silica, ammonia, phosphate, nitrate, and heavy metals. Many have color indicators that change color as the resins become exhausted. Products suitable for aquarium use are preferable as they have very low levels of toxic leachables. Some freshwater resins can be regenerated using warm salt water. Some saltwater resins can be regenerated on site, but they typically require strong acids or strong bases to do so and the hazardous chemical handling usually makes ion‐exchange filtration impractical in saltwater systems. Expended resins should be discarded through appropriate hazardous waste. These differ from conventional ion‐exchange water softeners, which produce high levels of sodium or potassium and are not designed for fish systems.

Reverse osmosis systems can remove ions from incoming freshwater. They use a semipermeable membrane to remove 90–99% of impurities such as chlorines, chloramines, nitrates, phosphates, pesticides, and heavy metals. Reverse osmosis does not remove as much as deionization, but in practical terms the resultant freshwater is similar for both processes. Deionized or reverse osmosis water may be used in systems containing fish that prefer soft, low‐pH water and in the cleaning of sensitive equipment.

Carbon dioxide (CO₂) scrubbers, injectors, or reactors can remove or add CO₂. These may be found on high‐density aquaculture systems and low‐pH fish systems. Carbon dioxide is produced through respiration. The amount of CO₂ in aquarium water affects the pH and alkalinity, since it becomes carbonic acid when dissolved in water. Too much carbonic acid lowers system pH, while too little increases pH.

If CO₂ is too high, it can be addressed with increased aeration (e.g. air diffusers, packed column aerators), addition of calcium hydroxide or sodium hydroxide solution, or use of a CO₂ scrubber. This is a device installed on the ambient air intake of an aeration device (e.g. air blower or foam fractionator) that contains an oxide or hydroxide media that absorbs CO₂ from the air before it is drawn into the system. A color indicator is used to determine when the media is exhausted. The media is not usually considered hazardous waste, but it can be exhausted rather quickly, which can become costly to manage on larger systems.

If CO₂ is too low, CO₂ injectors or reactors can be used to supplement CO₂ into the system. An injector typically uses a fine‐bubble diffuser to dissolve CO₂ directly into the water from a pressurized source such as a cylinder or dewar (vacuum flask). A reactor pre‐dissolves the pressurized gas into the system water in a reaction vessel outside of the aquarium. Both methods should use a CO₂ controller with pH as the control parameter.

Calcium injectors can inject calcium directly into a system in the form of calcium hydroxide solution. These are typically found on systems that house hard corals. Calcium reactors supplement calcium by separating calcium ion from carbonic acid in calcium carbonate media (like aragonite). This is done by bubbling pressurized CO₂ into it within a reaction vessel outside of the aquarium. Both methods should be pH‐controlled.