Unicel 4-Pack Anthony Apollo/Flowmaster Rectangular Pool Replacement Filter Grids Get the best replacement filter grids in the industry with 4 of these grid pool filters from Unicel Diotomatious Earth (DE) filter grids are used in Anthony Apollo 4000 and 5000 and Flowmaster 4000 and 5000 Effective at capturing microscopic debris and filters bacteria and contaminants Guaranteed perfect fit and simple installation Dimensions: 17.5 x 24 inches