ATTACHABLE ADDITIONAL FILTER FOR NANO CORNER FILTER AND NANO XL CORNER FILTER Especially recommended where fish are present. Increases filter capacity or can be used with phosphate binders or active carbon for short-term additional filtration. Simply fill, rinse (to remove possible residue caused by abrasion in transport) and clip on. For filling with Nano filter medium (Bio filter Granules/Algae Stop/Active Carbon).