Concisely removes harmful ions in series of events that are regularly repeated (5)
I believe the answer is:
cycle
'series of events that are regularly repeated' is the definition.
'cycle' can be an answer for 'series' (cycle is a kind of series). I'm not certain of the remainder of the definition.
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for cycle that I've seen before include "Recurring pattern of events" , "Revolution, ie one complete turn" , "Series; sequence" , "Repeated round of events" , "Recurring sequence" .)