A fish filter, also known as an aquarium filter, is usually a small filtering device inside or outside an aquarium to maintain the cleanliness of the water quality in the aquarium.

According to the filtration position, the fish filter can be divided into upper filtration, lower filtration, side filtration, and external filtration. Upper filtration and lower filtration are commonly used filtration methods, where upper filtration pumps water into the filtration container and then achieves filtration effect through overflow or drip flow; Lower filtration involves placing the filtered water tank in a cabinet below the fish tank, and then using the overflow principle to achieve the filtration effect. Side filtration is the placement of partitions inside the fish tank, using the internal space on the side or back of the tank, and utilizing the overflow principle to achieve filtration effects.

According to the different filter materials used, fish filters can be divided into physical filtration and biological filtration. The commonly used filter materials for physical filtration include white cotton and biochemical cotton, which can filter impurities, precipitates, etc; The commonly used filter materials for biological filtration include ceramic rings, which can cultivate beneficial bacterial communities such as nitrifying bacteria and remove harmful substances such as ammonia and nitrite.

When choosing a fish filter, it is necessary to consider factors such as the size, water volume, and water quality of the aquarium, as well as personal economic strength and preferences. It is recommended to choose a fish filter with good quality, significant effectiveness, low energy consumption, and easy cleaning.