oil spec

hi just bought my first t4 and gave it an oil change using recomended oil from halfords after a good run 300 miles or so the tappets seem a bit rattley which i didnt notice before the oil change wondered if this could be the oil or maybe it realy does need the tappets if so are they a big job...

Need to top mine up, does anyone know the correct type/rating for a 2.5tdi ExAA? Cheers :)