The Nu-Clear Model 1547 Extension Kit doubles the height of the Nu-Clear filters, allowing the use of twice as many bio balls. The extension kit for the Model 547, Biological Filter w/ Bio Balls includes bio balls. It expands the capability of the Model 547 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 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 547 with Extension Kit 1522, only use the Model 547 with the 1547 Extension Kit).