What was found
AIRCRAFT WAS GROUNDED: 2 MINUTES FROM LANDING THERE WAS A MUSTY SOCK SMELL ON THE FLIGHT DECK. FLIGHT ATTENDANTS SAID THEY DIDN'T SMELL IT BUT THERE WAS A VERY STRONG SMELL OF MARIJUANA IN THE CABIN THAT MASKED ANY OTHER ODORS. MAINTENANCE ACCOMPLISHED JOB CARD 26L00021001. NO ODOR WAS PRESENT WITH ENGINE BLEEDS OR APU BLEEDS RUNNING. WITH ENGINE BLEEDS OFF, APU BLEED OFF, AND CABIN FANS RUNNING, ODOR WAS PRESENT. MAINTENANCE INSPECTED AND FOUND CABIN RECIRCULATION FILTERS TO BE VERY DIRTY. REMOVED AND REPLACED CABIN RECIRCULATION FILTERS PER AMM 21-21-41. NO ODOR PRESENT WITH CABIN FANS RUNNING.