An apparatus for buoyancy driven filtration includes a tank and a filter assembly. The tank preferably includes a cylindrical sidewall, a circular base and a roof. The sidewall extends upward from the perimeter of the base wall and the roof extends across the top of the sidewall. A travel stop extends downward from the roof. A liquid feedstock flows through a storm water inlet. At least one overflow port is provided through the sidewall. The filter assembly includes a filter element and at least one buoyancy element disposed on a bottom of the filter medium. As water flows through the storm water inlet, the water finds its level above the filter medium to provide a liquid feedstock, some of which penetrates the filter medium to create a filtrate. As the tank fills, the filter assembly rises on top of the filtrate as provided by the buoyancy element.