hello m8 ive just joined and i am a profesional block paver by the look of the photo the joints havent been filled with kiln dried sand this realy needs to be added as it prevents any seeds etc. getting into the joints that act like a breeding ground . ithink i would sweep some sodium chlorite into the joints first then add the kiln died sand if possible run a compactor plate over the area before its swept off as this vibrates the sand into the joints if not just sweep it in but leave some on top a let the rain wash it down into the joints hope it helps.