Pondmaster 500, 9" x 9", Dual Mechanical & Biological Filter Box, With Removable Filter Cartridge, Low Profile, Less Obtrusive In The Pond, Features A Larger Filter For Less Cleaning, Offers Mechanical, Chemical, & Biological Filtration, Filter Media Is Easily Changed, Quick Disconnect For Easy Removal From Pump, Can Be Used With Many Submersible Pumps, For Use With Pumps Up To 500 GPH, For In Pond Use Only.