Definitions for "Under gravel filter"
A perforated plate placed on the bottom of the aquarium under the gravel. Water is pulled through the gravel, under the plate, and up through lift tubes. Provides superior biological filtration.
This filter provides both mechanical and biological filtration. It consists of a perforated plate placed on the bottom of the aquarium and then covered in gravel. Water is pulled through the gravel, under the plate, and up through lift tubes.
a classic down flow submerged bed filter
Keywords:  circulation, example, system
an example of a re-circulation system