A filtration system using lightweight fibrous media (LFM) that are pre-compressed either 1) manually; or 2) in-situ using hydraulic flow; and where the LFM are forced to separate and relax for cleaning either: 1) manually, 2) in-situ in their filter housing, or 3) in an auto-clean system using separate devices in order to enact a particularly aggressive cleaning process. A plurality of lightweight fibrous media balls are pre-compressed and used to form a single mass that can filter water as the media are compressed by pre-compression before installation, or by water flow pushing on a pre-compression plate during filtration thereby forming a single mass providing multitudes of tortuous paths through which water can flow and the media can capture small particulate matter.

A filtering apparatus has a volume-changeable filtering chamber having one or more flexible enclosing walls and receiving therein a compressible porous filtering medium, a fluid inlet coupled to the filtering chamber for introducing an input fluid stream with impurities into the filtering chamber, a fluid outlet coupled to the filtering chamber for discharging a filtered fluid stream from the filtering chamber, and a volume-changing structure coupled to or in association with the filtering chamber, adapted to permit increasing or decreasing of the volume of the filtering chamber so as to compress or decompress the compressible porous filtering medium therein so as to correspondingly adjust the pore size of the compressible porous filtering medium in said filtering chamber. A method for flushing a compressible filter media, and a method of variably adjusting the amount of filtering, is further disclosed and claimed.