It's generally a good idea to run the same fans on a radiator, so either get the same one, or replace all of them. If buying two+ of arctic p12 pro is same or cheaper than a single deepcool fk120, I'd go that route myself (especially since fk120 in retail is not the same fk120 that deepcool put on the aio, though, same story for many AIOs, vendors use higher rpm version fans on them).