A bleach roughly expired - nothing in it! (8)
I believe the answer is:
peroxide
'a bleach' is the definition.
(peroxide is a kind of bleach)
'roughly expired nothing in it' is the wordplay.
'roughly' indicates anagramming the letters.
'nothing' becomes 'o' (looks like zero - 0).
'in it' is an insertion indicator.
'expired' with letters rearranged gives 'perxide'.
'perxide' enclosing 'o' is 'PEROXIDE'.
(Other definitions for peroxide that I've seen before include "See 8" , "Chemical used to bleach hair" , "Hair-bleaching fluid" , "Hair treatment" , "Powerful bleaching agent" .)