Techniques for controlling drilling fluid cleaning apparatus that reclaim lost circulation material from spent drilling fluid are disclosed. In one embodiment, a system includes a tank, a density separation device, and a fluid density control system. The tank holds spent drilling fluid containing drilling fluid, lost circulation material, coarse solids and fine solids. The density separation device is coupled to an outlet of the tank. The density separation device provides an overflow stream and an underflow stream. The overflow stream contains less dense material than the underflow stream. The fluid density control system is configured to adjust the density of the spent drilling fluid provided to the density separation device by recirculating a portion of the underflow stream into the tank.