I'm a strong believer in not using filter socks other than when I blow off my rocks with a turkey baster. They're nitrate factories no matter how often you clean them out--hundreds of gallons of water per hour flowing through rotting material.
For those who don't believe they're nitrate factories, I've got a way to prove it. Clean out your skimmer's collection cup and run it for 24 hours with a filter sock and mark the level of skimmate collected. Then clean out the collection cup again and run it for 24 hours without a filter sock. You'll be amazed at the difference--there's about 5 times as much skimmate when running a filter sock. I know many people think the more skimmate the better, but in this case the larger amount is due to there being more ammonia available. Who knows how much of it manages to get past the skimmer?
Also, filter socks remove plankton from the water column, so they're impacting your food chain.