See 
If our fish are gasping and coming to the surface as if trying to breathe, it is an indication that something is wrong with the oxygenation of the aquarium. The much-appreciated CO2 must be taken care of and not let it escape easily.
It is through the phenomenon of osmosis that oxygen penetrates the water but it will only reach about 3 or 4 cm from the surface and it is necessary that it penetrates the entire aquarium space. There are plants that provide good oxygenation but they can also be dispensed with. The alternatives are suitable for both warmwater and coldwater fish.
In addition to fish and plants, there are very essential aerobic bacteria whose processes allow the plants to feed and provide oxygen to the fish. These bacteria feed on fish waste, uneaten food, dead fish and algae, but consume more oxygen than fish, so it is necessary to avoid overpopulation.
The appearance of anaerobic bacteria will produce the catastrophe of our fish, they gasp and die, the death also happens to the aerobic bacteria and the result is painful for the excess of population and for not having properly oxygenated the aquarium.
For a proper oxygenation we must use an aerator which will make that through the movement produced by the bubbles the oxygen that is on the surface is distributed throughout the length and breadth of the aquarium and other benefits. Life, whether fish, plants or bacteria, can be kept in balance if we give it due attention.
