The Nu-Clear Model 1530 Extension Kit doubles the height of the Nu-Clear filters, allowing the use of two cartridges. The extension kit for the Inland Seas Nu-Clear Model 530 Canister Filter, 30 sq. ft. 25 micron cartridge includes the extension housing and a 30 sq. ft. 25 micron poly-screen cartridge. It expands the capability of the Model 530 Canister Filter so it can handle freshwater and saltwater fish-only tanks up to 180 gallons and ponds up to 600 gallons.All extension kits include the body extensions, stainless steel band clamp, 1" mpt port plug, and a cartridge coupler. 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 530 with Extension Kit 1547, only use the Model 530 with the 1530 Extension Kit).