Blue Wave Portable Aero Spa Replacement Filter Cartridge- 4 Pack Replacement Filter Cartridge Dimensions: 4 x 4 x 4 1/2 Constructed of Reinforced Polyester Material That is Pleated and Strains the Water of Debris with Resin End Caps Filter Needs to Be Cleaned At Least Every 120 Hours Need to Be Replaced At Least Once a Month Depending on Use