It really depends on how much you feed as to how often they need to be changed IMO
, I feed lightly 3x a week and would change my socks out weekly but tree wasn't a whole lot for them to catch.
Now I could be wrong on this but I've always been under the impression that skimmers only remove organics once they've dissolved and are apart of the water column. So anything that's big enough robe caught by the sock is probably to big to be pulled out by the skimmer. IMHO
if your designing the sump yourself, set it up to accommodate both
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