What was found
AT JFK FLT 17, JFK TO FLL, ON TAKEOFF, B-HYDRAULIC SYSTEM LOW ECAM MESSAGE. ABORTED TAKEOFF AT APPROX 75 KTS, RETURNED TO GATE. FOUND BLUE SYSTEM LOW, FOUND NO EVIDENCE OF LEAK. SERVICED TO FULL, OPERATED ALL FLIGHT CONTROLS, UNABLE TO FIND LEAK AS PER AMM 27-50-00. LEAK CHECK GOOD, NO FAULT NOTED, OK FOR SERVICE.