Column Pairs should only be replaced as needed. When replacement is required the InogenOne G4 will alert you to the need with a Low Priority Alert reading "O2 Service Soon". This alert means that the columns should be replaced within 30-days. Column replacement is a simple process, that can be completed at home, without any special tools. For full instructions see the "Column Change Procedure" section of Chapter 6 of the InogenOne G4 User Manual. It is strongly recommended to purchase this item for immediate use, not for storage.