The oil film in the fish tank is made up of dust, oil pollution, in the water film is mainly by dust, oil, excreta, residual feeds, dead fish and decomposition products of small biological residues, in which much is protein and protein. The more protein in the water, more norganic nitrogenous compounds will be in the water. The harm will be larger when the hydrogen nitride and nitrite is more.
The reason why the bubble on the fish tank does not break is because that the water is eutrophic, which can be solved by increasing filtration, reducing feed intake or frequently changing the water.
The environment of fish tank is the same with the sea. When it is contaminated or the self-renewal ability reduces (for example when the water is seldom changed), water will be eutrophication. Besides, sunshine is plenty and green algae overgrowths, which will consume a large amount of dissolved oxygen in water. This is the principle of green tide.
