Extension kit for the Inland Seas Nu-Clear Model 533 Canister Filter, 25 Micron Cartridge. Kit includes extension housing, and a 30 sq. ft. 25 micron cartridge. Expands the capability of the Model 522 Canister Filter so it can handle freshwater and saltwater fish-only tanks up to 180 gallons and ponds up to 600 gallons.Nu-Clear 500 Series Extension Kit Features: The Extension Kits kits double the height of the Nu-Clear filters, allowing the use of two cartridges. All extension kits include the body extensions, stainless steel band clamp, 1" mpt port plug, and a cartridge coupler (if required). 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 522 with Extension Kit 1547, only use the Model 522 with the 1522 Extension Kit).