Abstract: A fluid storage tank assembly comprising a wall assembly, a floor assembly and a roof assembly. The wall assembly providing a thermal insulating layer comprising two or more wall sub-assemblies removably stacked on top of each other that circumscribe an interior chamber of the tank assembly. Each wall sub-assembly comprises a plurality of removably interconnected wall panels circumscribing a portion of the interior chamber. The wall assembly is configured to house a liner for containing a fluid. The floor assembly bounds a bottom portion of the interior chamber and provides a thermal insulating layer. The roof assembly bounds a top portion of the interior chamber and provides a thermal insulating layer.