I don't use a filter sock. The overflow is diverted to my refugium and mangrove tank. In general my fish catch most of the food before it hits the overflow and I figure that anything else that slips by can feed all the critters in the refugium. I have tons of isopods, amphipods, starfish, bristle worms, snails, and red spagehti worms that clean everything up in there. I have tested my nitrates and they are 0. As for micro bubbles they have never been a problem. The only time I throw in a filter sock is if I am doing maintenance that throws up a lot of sediment.