OEM quality replacement filter cartridge for Dynamic Series I, Series II, Series III, Series IV & Waterway. Replacement filter cartridges from Pleatco are manufactured using the highest quality raw materials. Durable end caps & unparalleled resistance to harsh water treatment chemicals help Pleatco filter cartridges last longer than other replacements. A properly designed "Free Flow" center core provides 20% more efficient water flow than a simple drilled PVC core you might have in your filter today. While it may not seem like much, a more efficient water flow results in less wear on your pump & ultimately saves you money in energy costs from running the filter system for shorter periods of time.