Cheers for all the feedback ladies and gentlemen.
New filter arrived today with a 100ml bag of Seachem Purigen, and after a painful and highly annoying hour of installation due to me having very limited side and zero back access, it's up and running. Flow rate is much better and the Purigen is doing it's job.
If my Cichlids are in a friendly enough mood I'll have some photos of them up for you shortly.