Thanks everyone.
My system is configured such that the skimmer is gravity fed from the overflows. THe flow is split, part to the skimmer and part directly to a small refugium section. At the moment, the effluent from the skimmer goes through a sock - it gets quite gunky after 4-5 days. The flow to the refugium on the other hand has no sock - and there's quite a lot of detritus and silt in that section as a result.
So I was going to run both through socks. Seems the camp would be split 50-50 on my proposal. But in a bare bottom tank, there is nowhere for particulates to settle - and so unless you remove them it seems like there is constantly "bits" in the water column. You expect this in something like a FOWLR but in the supposed pristine conditions of an SPS tank......