Fluval "U2" underwater filter with three stage filtration is ideal for use in fresh, marine or reptile environments. Stage 1 foam removes large particles. Stage 2 poly/carbon cartridge traps fine debris, improves water clarity and removes impurities. Stage 3 BIOMAX provides optimal biological filtration efficiency. Fluval U2 underwater filter offers a Flip-Top for quick and easy maintenance and an adjustable 3 way flow for output flexibilty . Suitable for aquariums from 12-30 US gal.