I ordered these for the first time and I hate it. I purchased the 100 micron sock. It never seems to stay under water and it does not catch the fine particles. My water has gotton cloudy, my sump is dirty which it never is when I use the "cotton" (don't know material) filter. I disassembled my skimmer about a month ago to give it a good clean (I do this approx. every 6 months), now I have to do it sooner cause there is a whole bunch of crap sitting inside of it.