TFT's SHO-FLOW 2 LOW FLOW BLUETOOTH® generates its own power using an unobstructed water driven turbine, with a built in stream straightener, that will pass debris up to 1.7" (43 mm) in diameter. Starting at 100 GPM (400 l/min), the turbine generates power needed to supply a BLUETOOTH® connection to any smart device. Choose units you want displayed from your smart device; gpm, gps, l/min or l/sec. Full flow range 100 - 500 gpm (1.7 - 8.3 gps) (400 - 2000 l/min) (3.33 - 19.16 l/sec)