Settleable-particles are separated from a dirty flow of settleable-particles and fluid by trays having a planar section configured with opposed ends and opposed sides, and an entrance edge and an exit edge on opposed ends. The section has opposed side edges, and an upturned entrance lip at each of the entrance and exits edges, with downturned lips at each side edge. A settler unit has one tray as an upper tray and another tray as a lower tray, the two trays being mounted parallel and at a low-angle to define a dirty flow entrance, a clean flow exit, and a pocket between the upturned entrance lip and the upturned exit lip for receiving and capturing settled-particles from the dirty flow while cleaner flow flows from the entrance to the exit. A sludge exit is at each side of the trays for permitting the captured settled-particles to exit the pocket.