I change out my filter socks a few times a week generally. Your live rock and sand are where the biological filtration takes place. the sock is just getting particulate matter out of the water. changing out the sock may even help reduce nitrates since the stuff that the sock caught cant rot away.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.