For those like myself who have aquariums of 60 gallons or less and no room for a sump, the AquaMaxx HF-M filter/skimmer combine is a really great filtration system. It comes with some biological filter media and has a large compartment which may be used as a refugium or additional biological filtration. I am thoroughly pleased with the unit's operation; the skimmer works great on my 60 gallon.