Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 110

Maintaining an appropriate balance of dissolved gases in fish systems is critical to support animal respiration, support microbial respiration within the biological filtration, maintain pH, and prevent gas supersaturation. The most critical dissolved gases are oxygen, nitrogen, and carbon dioxide. Based on individual gas solubility, their natural ratio in water is 1:2:4 respectively. The ratio and actual gas concentration depend on atmospheric pressure, water temperature, salinity, pH, biological activity, and gas exchange at the surface. The larger the surface area:volume ratio of an aquarium, pond, filter, or sump, the more potential there is for gas exchange. Movement at the water surface (e.g. air columns, pump returns at the surface, and surface skimmers) enhances gas exchange at the surface. Surface skimming action is particularly important, as it prevents accumulation of a film of surfactant material at the air/water interface that reduces gas exchange.

The primary components that maintain adequate gas exchange include:

 Air/oxygen diffusers, e.g. air stones connected to ambient air or compressed oxygen (Figure A3.1a).

 Air/oxygen exchange towers, e.g. degas towers (Figure A3.1b).

 Surface skimmers that remove the surface water.

 Air/oxygen venturis that suck in air or oxygen.

Supersaturation can occur whenever gas gets into a system at high pressure. The most common causes are compromised plumbing on the suction side of a pump, excessive deep‐water aeration, or supersaturated incoming water. The percentage of supersaturation (delta P) is equal to the total dissolved gases (TDGs) compared to the barometric pressure of the air at the water's surface. This is measured using TDG meters (also known as saturometers). A delta P greater than 10% can cause gas emboli in fish (see Chapter C1).