Oxygen in the Marine Aquarium Nitrogen is important in aquarium conditions because of the introduction of nitrogenous material as food and conversion by the nitrifying bacteria, but is less important in the sea. Carbon dioxide is highly soluble in seawater. It will enter the water through the respiratory activities of fish, invertebrates, algae and bacteria. It will leave the water by atmospheric interchange at the surface, or by complex chemical reactions with other elements in the 'Carbon Cycle'. Living Animals and Plant Life.
Real seawater contains masses of invisible planktonic life.
In Spring the inland waters surrounding the British Isles may be coloured brown by naturally occurring blooms of phytoplankton. In collected seawater, this phytoplankton can die within one hour and rapidly turn the water toxic. Natural seawater also contains bacteria and there is a theoretic chance of introducing pathogens, including free-swimming stages of parasitic animals such as Cryptocotyle lingua. Dissolved Organic Waste Marine creatures excrete soluble waste, urea, ammonia etc., which will be present in small quantities in seawater, but larger proportions are likely in aquarium conditions. After storms or in the vicinity of dredging operations, seawater is likely to contain suspended silt or sand from the bed of the sea.