The Nu-Clear Model 1566 Extension Kit doubles the height of the Nu-Clear filters allowing the use of twice as much activated carbon. The extension kit for the Nu-Clear Model 566 Activated Carbon Filter includes a 7 lb bag of Inland Seas Marine and Reef activated carbon.The extension kits include the body extensions, stainless steel band clamp and 1" mpt port plug. Extensions kits include a plug for the redundant inlet on the bottom filter. It is not recommended to mix different types of cartridges or media (i.e. Do not use a Model 566 with Extension Kit 1530, only use the Model 566 with the 1566 Extension Kit).